Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3018882

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019276

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019453

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.3019327

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Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

In this study, we successfully applied a transition-edge sensor (TES) spectrometer as a detector for microbeam X-ray measurements from a synchrotron X-ray light source in hard X-ray region to determine...

DOI： 10.1039/d4an00059e

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present timing and spectral analysis results of the NICER and NuSTAR observations of the dwarf nova MASTER OT J030227.28+191754.5 during the 2021–2022 outburst. The soft X-ray component was found to be dominated by blackbody radiation with a temperature of ∼30 eV and also showed prominent oxygen and neon emission lines. The blackbody luminosity exceeded 10³⁴ erg s⁻¹, which is consistent with theoretical predictions, and then decreased more than an order of magnitude in 3.5 days. The inferred abundances of oxygen and neon in the optically thin coronal region surrounding the central white dwarf (WD) are several times higher than the respective solar values. Although inconclusive, the abundance enrichment may originate from the WD, indicating that it may be mainly composed of oxygen and neon. Assuming that the blackbody radiation comes from the belt-shaped boundary layer between the WD and the accretion disk, we estimated the WD radius to be (2.9 ± 1.1) × 10⁸ cm, which corresponds to the WD mass range of 1.15–1.34 M_⊙. If the accretion continues for another ∼1 Gyr, the WD may experience an accretion-induced collapse into a neutron star and form a so-called black widow pulsar system.

DOI： 10.3847/1538-4357/acd933

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acd933/pdf

Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

Richardson–Lucy (RL) deconvolution is one of the classical methods widely used in X-ray astronomy and other areas. Amid recent progress in image processing, RL deconvolution still leaves much room for improvement under realistic situations. One direction is to include the positional dependence of a point-spread function (PSF), so-called RL deconvolution with a spatially variant PSF (RL_sv). Another is the method of estimating a reliable number of iterations and their associated uncertainties. We developed a practical method that incorporates the RL_sv algorithm and the estimation of uncertainties. As a typical example of bright and high-resolution images, the Chandra X-ray image of the supernova remnant Cassiopeia A was used in this paper. RL_sv deconvolution enables us to uncover the smeared features in the forward/backward shocks and jet-like structures. We constructed a method to predict the appropriate number of iterations using statistical fluctuation of the observed images. Furthermore, the uncertainties were estimated by error propagation from the last iteration, which was phenomenologically tested with the observed data. Thus, our method is a practically efficient framework to evaluate the time evolution of the remnants and their fine structures embedded in high-resolution X-ray images.

DOI： 10.3847/1538-4357/acd9b3

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/acd9b3/pdf

Publishing type：Research paper (scientific journal)  

Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonic noise caused by the mechanical coolers is a general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the Resolve instrument to be flown on the XRISM satellite. Resolve is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to ∼ 4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule–Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (< 20 Hz) frequency beat between the 4th JTC and 14th STC harmonics and the 7th JTC and the 23–24th STC harmonics. We present here a description and interpretation of these measurements.

DOI： 10.1007/s10909-022-02935-1

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevlett.130.173001

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.130.173001/fulltext

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.aca.2022.340755

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Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2022.117962

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10909-022-02910-w

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Other Link： https://link.springer.com/article/10.1007/s10909-022-02910-w/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

DOI： 10.1007/s10909-022-02860-3

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Other Link： https://link.springer.com/article/10.1007/s10909-022-02860-3/fulltext.html

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2629066

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2630654

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2629086

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We examined the X-ray and radio spatial structure at the eastern ear of the W 50/SS 433 system to clarify a characteristic feature of the termination region of the SS 433 jet, and found that a hot spot ahead of the filament structure, which is considered to be a terminal shock of the SS 433 eastern jet, is clearly different from a single point source. The detailed spatial structure of the X-ray emission is finely resolved by Chandra observations, showing that there are two sources. By comparing the point-spread function of Chandra with the radial profiles of the two sources, the northern one is clearly more extended than a point source while the other seems marginally extended. Since there are no point sources nearby, the northern hot spot is likely a localized diffuse source. The northern hot spot spatially corresponds to the peak of the radio emission. Its spatial correlation is confirmed by an X-ray image using XMM-Newton. The X-ray spectra of the two sources are reproduced by a single absorbed power-law but the column density of the northern part is larger by a factor of similar to 3. When a radiation model comprising synchrotron emission and inverse Compton emission is applied to the spectral energy distribution of the northern hot spot, the emission from this spot can be explained by the radiation from an electron population accelerated up to 30 TeV in a magnetic field strength of B less than or similar to 50 mu G. This model also agrees with the radio and X-ray data, as well as the upper limit of gamma-ray emission obtained by the Fermi satellite.

DOI： 10.1093/pasj/psac011

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Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/ac6e63

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We report on simultaneous optical and X-ray observations of the dwarf nova SS Cyg with Tomo-e Gozen/1.05 m Kiso Schmidt and Neutron star Interior Composition ExploreR (NICER)/International Space Station (ISS). A total of four observations were carried out in the quiescent state and highly correlated light variations between the two wavelengths were detected. We have extracted local brightness peaks in the light curves with a binning interval of 1 s, called “shots,” and have evaluated time lags between the optical and X-ray variations by using a cross-correlation function. Some shots exhibit significant optical lags to X-ray variations and most of them are positive, ranging from +0.26 to +3.11 s, which have never been detected. They may be ascribable to X-ray reprocessing in the accretion disk and/or the secondary star. This analysis is possible thanks to the high timing accuracy and the high throughput of NICER and the matching capability of Tomo-e Gozen. Also, it is confirmed that the correlation between the optical and X-ray variations changed in the middle of one of our observation windows and that the X-ray spectrum softer than 2 keV varied in accordance with the correlation.

DOI： 10.1093/pasj/psac027

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10909-022-02719-7

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Other Link： https://link.springer.com/article/10.1007/s10909-022-02719-7/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

The origin of the jet-like structures observed in Cassiopeia A is still unclear, although it seems to be related to its explosion mechanism. X-ray observations of the characteristic structures could provide us useful information on the explosive nucleosynthesis via the observation of elements, which is a unique approach to understand its origin. We here report the discovery of shocked stable Ti, which is produced only at the inner region of exploding stars, in the northeast jet of Cassiopeia A using the 1 Ms deep observation with the Chandra X-ray observatory. The observed Ti coexists with other intermediate-mass elements (e.g., Si, S, Ar, Ca) and Fe at the tip of the X-ray jet structure. We found that its elemental composition is explained well with the production by the incomplete Si burning regime, indicating that the formation process of the jet structure was sub-energetic at the explosion (the peak temperature during the nuclear burning must be ≲5 × 109 K at most). Thus, we conclude that the energy source that formed the jet structure was not the primary engine for the supernova explosion. Our results are useful to limit the power of the jet-structure formation process, and a weak jet mechanism with low temperature may be needed to explain it.

DOI： 10.1093/pasj/psab130

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevlett.128.112503

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevLett.128.112503/fulltext

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The Resolve instrument onboard the XRISM satellite is equipped with 6 x 6 x-ray microcalorimeter detectors aiming at an energy resolution of 7 eV (FWHM) at 5.9 keV. It is currently under development by an international collaboration and will be launched in 2023. The detectors are operated at 50 mK, which is achieved by a combination of four Stirling coolers (STC), one Joule-Thomson cooler (JTC), three-stage adiabatic demagnetization refrigerators, and superfluid helium inside the dewar. The cryocoolers (STC and JTC) are significant sources of microphonic noise against the detector performance. To understand and characterize the microphonic propagation, we monitored the level of vibration throughout the ground instrument-level tests in 2019-2022, yielding a rich and unique data set of the accelerometers and the detector at 50 mK amounting to 1720 hours (6.2 Ms). In this article, we report the result of classifying thermal and non-thermal microcalorimeter noise, distinguishing the origin of the noise, and the method for optimizing the cooler drive frequency that minimizes the effect of the noise originating from the cooler.

DOI： 10.1117/12.2629773

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The spectroscopic performance of x-ray instruments can be affected at high count rates. The effects and mitigation in the optical chain, such as x-ray attenuation filters or de-focusing mirrors, are widely discussed, but those in the signal chain are not. Using the Resolve x-ray microcalorimeter onboard the XRISM satellite, we discuss the effects observed during high count rate measurements and how these can be modeled. We focus on three instrumental effects that impact performance at high count rate: CPU limit, pile up, and electrical cross talk. High count rate data were obtained during ground testing using the flight model instrument and a calibration x-ray source. A simulated observation of GX 13+1 is presented to illustrate how to estimate these effects based on these models for observation planning. The impact of these effects on high count rate observations is discussed.

DOI： 10.1117/12.2628784

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/tasc.2021.3067793

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Arrays of superconducting transition-edge sensor (TES) microcalorimeters are attractive for someX-ray experiments where the combination of higher collection efficiency than crystal spectrometers and much better energy resolution than semiconductor detectors is enabling. For hard X-ray (>2 keV) applications, a TESis often integratedwith an extra absorber to extend its dynamic range, quantum efficiency and collecting area. For >100 keV applications, millimeter size absorbers have been manually attached to TES pixels after fabrication. At lower energies, the absorber size needs to be much smaller, because a large heat capacity degrades energy resolution. In that case, the absorber is directly electroplated or evaporated on the TES during the fabrication process. In this work, we present TES microcalorimeters optimized for the intermediate hard X-ray energy region (20 keV similar to 100 keV) that have thick absorbers directly deposited during the TES fabrication process. This microcalorimeter is designed to measure high-resolution muonic atom transition X-ray spectra as a method to study quantum electrodynamics (QED) effects. The absorber is comprised of evaporated gold and electroplated bismuth layers and is designed to optimize dynamic range, collecting efficiency, and energy resolution in the 20 keV to 45 keVenergy range. Aprototype with pure gold absorbers has been fabricated and characterized, in order to obtain a first experimental reference in the detector development process.

DOI： 10.1109/TASC.2021.3059972

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Publishing type：Research paper (scientific journal)  

We observed electronic K x rays emitted from muonic iron atoms using superconducting transition-edge sensor microcalorimeters. The energy resolution of 5.2 eV in FWHM allowed us to observe the asymmetric broad profile of the electronic characteristic Kα and Kβ x rays together with the hypersatellite Khα x rays around 6 keV. This signature reflects the time-dependent screening of the nuclear charge by the negative muon and the L-shell electrons, accompanied by electron side feeding. Assisted by a simulation, these data clearly reveal the electronic K- and L-shell hole production and their temporal evolution on the 10-20 fs scale during the muon cascade process.

DOI： 10.1103/PhysRevLett.127.053001

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
SS Cyg has long been recognized as the prototype of a group of dwarf novae that show only outbursts. However, this object has entered a quite anomalous event in 2021, which at first appeared to be standstill, i.e., an almost constant luminosity state observed in Z Cam-type dwarf novae. This unexpected event gives us a great opportunity to reconsider the nature of standstill in cataclysmic variables. We have observed this anomalous event and its forerunner, a gradual and simultaneous increase in the optical and X-ray flux during quiescence, through many optical telescopes and the X-ray telescopes NICER and NuSTAR. We have not found any amplification of the orbital hump during quiescence before the anomalous event, which suggests that the mass transfer rate did not significantly fluctuate on average. The estimated X-ray flux was not enough to explain the increment of the optical flux during quiescence via X-ray irradiation of the disk and the secondary star. It would be natural to consider that viscosity in the quiescent disk was enhanced before the anomalous event, which increased mass accretion rates in the disk and raised not only the optical flux but also the X-ray flux. We suggest that enhanced viscosity also triggered the standstill-like phenomenon in SS Cyg, which is considered to be a series of small outbursts. The inner part of the disk would always stay in the outburst state and only its outer part would be unstable against the thermal–viscous instability during this phenomenon, which is consistent with the observed optical color variations. This scenario is in line with our X-ray spectral analyses which imply that the X-ray-emitting inner accretion flow became hotter than usual and vertically expanded, and that it became denser and was cooled down after the onset of the standstill-like state.

DOI： 10.1093/pasj/psab073

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Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.35.011006

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present X-ray analysis of the ejecta of supernova remnant (SNR) G350.1-0.3 observed with Chandra and Suzaku, clarify the ejecta's kinematics over a decade, and obtain a new observational clue to understanding the origin of the asymmetric explosion. Two images from Chandra X-ray Observatory taken in 2009 and 2018 are analyzed with several methods and enable us to measure the velocities in the plane of the sky. A maximum velocity is 4640 +/- 290 km s(-1) (0.218 +/- 0.014 arcsec yr(-1)) in the eastern region in the remnant. These findings trigger us to scrutinize the Doppler effects in the spectra of the thermal emission, and the velocities in the line-of-sight direction are estimated to be 1000 km s(-1). The results are confirmed by analyzing the spectra of Suzaku. Combining the proper motions and line-of-sight velocities, the ejecta's 3D velocities are similar to 3000-5000 km s(-1). The center of the explosion is more stringently constrained by finding the optimal time to reproduce the observed spatial expansion. Our findings that the age of the SNR is estimated at most to be 655 yr and the CCO is observed as a point source object against the SNR strengthen the "hydrodynamical kick" hypothesis on the origin of the remnant.

DOI： 10.3847/1538-4357/abf2bd

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Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0020642

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Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2560819

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. A novel triggering function developed for 240-pixel Transition-Edge Sensors is demonstrated under the high rate of particle background. The function is integrated into the standard data acquisition system in the NIST TES framework. It enables any type of combination of trigger pattern when a pixel is triggered, which is called “group trigger.” As a practical implementation, the primary trigger is distributed to the four physically nearest pixels. The group trigger function was utilized throughout the entire one-month J-PARC experiment for the measurement of the Kaonic-atom X-rays. This trigger allowed us to confirm that the increased background and degraded energy resolution we observed when operating the TES array in the presence of an ion beam are the result of thermal crosstalk from charged particles. We show that the maximum of the average of the signals among the neighboring four pixels is useful for event selection. We use cuts based on this parameter to improve the peak-to-background level in a measured x-ray energy spectrum by a factor of ∼ 2, while keeping 95% of measured events. This flexible group triggering technique allows us to improve the signal to noise on the very faint Kaonic Helium x-ray lines we are measuring, better understand our experiment environment, and we believe this technique may prove useful in other ground and space-based TES applications.

DOI： 10.1007/s10909-020-02468-5

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02468-5/fulltext.html

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. High-energy-resolution X-ray spectroscopy using X-ray microcalorimeters has been widely adopted for high-precision experiments on fundamental science. The technical difficulties come from its use at low temperatures and its high sensitivity to the external environment, though many countermeasures have been proposed through the experience of space applications. The limit of the number of pixels of the semiconductor-type X-ray microcalorimeters can be solved by using the transition-edge sensor (TES) superconducting detector. Recently, a study of the strong nuclear force via high-energy-resolution X-ray spectroscopy of kaonic atoms using TES at the J-PARC accelerator facility was successfully performed by the HEATES collaboration. Furthermore, muonic-atom spectroscopy using TES has been demonstrated at the J-PARC muon facility, and a physical experiment to test the electromagnetic force under a strong electric field is ready for commissioning. Material diagnostics at a hard X-ray synchrotron facility have been tested at SPring-8 and resulted in a successful operation for the first time. Other than X-rays, TES has been used as a mass spectrometer for neutral molecules in a cryogenic electrostatic ion ring. The entire design of the experiment is carefully considered to meet the science-specific requirement. We will summarize the latest and future applications of the microcalorimeter and present key technologies, such as digital electronics, data acquisition software, aperture, collimator, mechanical, and electrical interface. Our results will be helpful for other users to design new experiments for fundamental science.

DOI： 10.1007/s10909-020-02441-2

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02441-2/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0016333

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10909-020-02476-5

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02476-5/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. Exotic atom experiments place transition-edge sensor (TES) microcalorimeter arrays in a high-energy charged particle-rich environment. When a high-energy charged particle passes through the silicon substrate of a TES array, a large amount of energy is deposited and small pulses are generated across multiple pixels in the TES array due to thermal crosstalk. We have developed analysis techniques to assess and reduce the effects of charged particle events on exotic atom X-ray measurements. Using this technique, the high-energy and low-energy components of the X-ray peaks due to pileup are eliminated, improving the energy resolution from 6.6 to 5.7 eV at 6.9 keV.

DOI： 10.1007/s10909-020-02484-5

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02484-5/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

We integrated a TES X-ray spectrometer with a charged kaon beam line at J-PARC to perform X-ray spectroscopy of kaonic helium atoms. Limited beam intensity and a broad beam spot size made it crucial to increase the detector acceptance angle as much as possible, requiring significant development. To this end, our TES system shared the same vacuum with a cryogenic system of the liquid helium experimental target. We also specially developed a target cell for liquid helium and a thinned aperture array on top of the TES detector. Additionally, thermal and magnetic shields and infrared filters were optimized in terms of a larger acceptance angle and energy resolution of the detector. The scientific campaign was performed in June, 2018, where the whole system was stably operated for almost one month.

DOI： 10.1007/s10909-020-02434-1

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02434-1/fulltext.html

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

© 2020, Springer Science+Business Media, LLC, part of Springer Nature. A useful function, called group trigger, is implemented in a data acquisition system of a 240-pixel X-ray transition-edge sensor array to store simultaneous waveforms from any desired set of pixels. It works as a diagnostic tool which can record both primary pulses and associated crosstalk events with enough freedom to optimize the data output. Under a high rate of charged particle background, such as in an accelerator, investigating signals from any combination of trigger patterns for a particular event is of high importance. We utilized this function throughout an entire experiment at J-PARC, measuring kaonic atom X-rays in 2018. This was the first time a group trigger was applied to exotic-atom spectroscopy. In this experiment, the primary trigger was distributed to the four physical nearest neighbor pixels for practical purposes. The function clarified the effect of thermal and electrical cross talk from X-rays and charged particles, resulting in a better understanding of the behavior of the TES array in such a high-background environment.

DOI： 10.1007/s10909-020-02449-8

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02449-8/fulltext.html

Publishing type：Research paper (international conference proceedings)  

We are studying an improved DIOS (Diffuse Intergalactic Oxygen Surveyor) program, Super DIOS, which is accepted for establishing the Research Group in ISAS/JAXA, for a launch year after 2030. The aim of Super DIOS is an X-ray quantitative exploration of”dark baryon” over several scales from circumgalactic medium, cluster outskirt to warm-hot intergalactic medium along the Cosmic web with mapping redshifted emission lines from mainly oxygen and other ions. These observations play key roles for investigating the physical condition, such as the energy flow and metal circulation, of most baryons in the Universe. This mission will perform wide field X-ray spectroscopy with a field of view of about 0.5-1 degree and energy resolution of a few eV with TES microcalorimeter, but with much improved angular resolution of about 10-15 arcseconds. We will also consider including a small gamma-ray burst monitor and a fast repointing system. We will have an international collaboration with US and Europe for all the onboard instruments.

DOI： 10.1117/12.2561681

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/mnras/stz1528

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Reliable results when fitting X-ray data require proper consideration of the statistics involved. We probe the impact of Gaussian versus Poisson statistics at low count levels using both the standard chi(2) method and maximum likelihood based on Poisson (C) statistics. The difference is studied and quantified through simulated spectra with known properties. We then test the results through analysis of Mn K alpha calibration data taken with the flight spare microcalorimeter for the Hitomi soft X-ray spectrometer. Through comparison with simulations, our results show that the chi(2) method tends to give overly optimistic estimates of the detector energy resolution, in particular when there are few counts. Given an energy resolution of similar to 5eV and a line with about 100 photons, the line width becomes similar to 10% lower in the chi(2) method than in Poisson statistics. This is a consequence of the uncertainties being dominated by counting statistics, and therefore highlights the need to choose the appropriate fit statistic.

DOI： 10.1093/pasj/psz053

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.74.1.0_745

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

We are developing transition edge sensor (TES) X-ray microcalorimeters for the future Japanese mission DIOS. It adopts microstrip readout wiring for low pixel-to-pixel crosstalk. In past samples, TES films composed of Ti and Au have not shown proper super–normal transition when it is deposited on the wiring. Assuming that surface roughness of the substrate can influence the transition, we reduced the surface roughness of the underneath layer before deposition of the TES film by using chemical mechanical polishing. We then found that the substrate becomes much smoother with a roughness of &lt
1 nm rms and the TES film shows a proper transition.

DOI： 10.1007/s10909-018-1995-z

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psy027

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

The updated program of the future Japanese X-ray satellite mission Diffuse Intergalactic Oxygen Surveyor (DIOS), called as Super DIOS, is planned to search for dark baryons in the form of warm–hot intergalactic medium (WHIM) with high-resolution X-ray spectroscopy. The mission will detect redshifted emission lines from OVII, OVIII and other ions, leading to an overall understanding of the physical nature and spatial distribution of dark baryons as a function of cosmological timescale. We have started the conceptual design of the satellite and onboard instruments, focusing on the era of 2030s. The major change will be an improved angular resolution of the X-ray telescope. Super DIOS will have a 10-arcsec resolution, which is an improvement by a factor of about 20 over DIOS. With this resolution, most of the contaminating X-ray sources will be separated, and the level of the diffuse X-ray background will be much reduced after subtraction of point sources. This will give us higher sensitivity to map out the WHIM in emission.

DOI： 10.1007/s10909-018-1918-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

We present data preprocessing based on an artificial neural network to estimate the parameters of the X-ray emission spectra of a single-temperature thermal plasma. The method finds appropriate parameters close to the global optimum. The neural network is designed to learn the parameters of the thermal plasma (temperature, abundance, normalization and redshift) of the input spectra. After training using 9000 simulated X-ray spectra, the network has grown to predict all the unknown parameters with uncertainties of about a fewper cent. The performance dependence on the network structure has been studied. We applied the neural network to an actual high-resolution spectrum obtained with Hitomi. The predicted plasma parameters agree with the known best-fitting parameters of the Perseus cluster within uncertainties of ≲10 per cent. The result shows that neural networks trained by simulated data might possibly be used to extract a feature built in the data. This would reduce human-intensive preprocessing costs before detailed spectral analysis, and would help us make the best use of the large quantities of spectral data that will be available in the coming decades.

DOI： 10.1093/mnras/sty161

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

The X-ray Astronomy Recovery Mission (XARM) is a recovery mission of ASTRO-H/Hitomi, which is expected to be launched in Japanese Fiscal Year of 2020 at the earliest. The Resolve instrument on XARM consists of an array of 6 × 6 silicon-thermistor microcalorimeters cooled down to 50 mK and a high-throughput X-ray mirror assembly with the focal length of 5.6 m. Hitomi was launched into orbit in February 2016 and observed several celestial objects, although the operation of Hitomi was terminated in April 2016. The soft X-ray spectrometer (SXS) on Hitomi demonstrated high-resolution X-ray spectroscopy of ~ 5 eV FWHM in orbit for most of the pixels. The Resolve instrument is planned to mostly be a copy of the Hitomi SXS and soft X-ray telescope designs, though several changes are planned based on the lessons learned from Hitomi. We report a brief summary of the SXS performance and the status of the Resolve instrument.

DOI： 10.1007/s10909-018-1913-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE-SOC PHOTO-OPTICAL INSTRUMENTATION ENGINEERS  

The Soft X-ray Spectrometer onboard the Astro-H (Hitomi) orbiting x-ray observatory featured an array of 36 silicon thermistor x-ray calorimeters optimized to perform high spectral resolution x-ray imaging spectroscopy of astrophysical sources in the 0.3-to 12-keV band. Extensive preflight calibration measurements are the basis for our modeling of the pulse height-energy relation and energy resolution for each pixel and event grade, telescope collecting area, detector efficiency, and pulse arrival time. Because of the early termination of mission operations, we needed to extract the maximum information from observations performed only days into the mission when the onboard calibration sources had not yet been commissioned and the dewar was still coming into thermal equilibrium, so our technique for reconstructing the per-pixel time-dependent pulse height-energy relation had to be modified. The gain scale was reconstructed using a combination of an absolute energy scale calibration at a single time using a fiducial from an onboard radioactive source and calibration of a dominant time-dependent gain drift component using a dedicated calibration pixel, as well as a residual time-dependent variation using spectra from the Perseus cluster of galaxies. The energy resolution was also measured using the onboard radioactive sources. It is consistent with instrument-level measurements accounting for the modest increase in noise due to spacecraft systems interference. We use observations of two pulsar wind nebulae to validate our models of the telescope area and detector efficiency and to derive a more accurate value for the thickness of the gate-valve Be window, which had not been opened by the time mission operations ceased. We use observations of the Crab nebula to refine the pixel-to-pixel timing and validate the absolute timing. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.

DOI： 10.1117/1.JATIS.4.2.021407

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© The Authors. The Hitomi (ASTRO-H) mission is the sixth Japanese x-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft x-rays to gamma rays. After a successful launch on February 17, 2016, the spacecraft lost its function on March 26, 2016, but the commissioning phase for about a month provided valuable information on the onboard instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.

DOI： 10.1117/1.JATIS.4.2.021402

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

The Astro-H (Hitomi) Soft X-ray Spectrometer (SXS) was a pioneering imaging x-ray spectrometer with 5 eV energy resolution at 6 keV. The instrument used a microcalorimeter array at the focus of a high-Throughput soft x-ray telescope to enable high-resolution nondispersive spectroscopy in the soft x-ray waveband (0.3 to 12 keV). We present the suite of ground calibration measurements acquired from 2012 to 2015, including characterization of the detector system, anti-coincidence detector, optical blocking filters, and filter-wheel filters. The calibration of the 36-pixel silicon thermistor microcalorimeter array includes parameterizations of the energy gain scale and line-spread function for each event grade over a range of instrument operating conditions, as well as quantum efficiency measurements. The x-ray transmission of the set of five Al/polyimide thin-film optical blocking filters mounted inside the SXS dewar has been modeled based on measurements at synchrotron beamlines, including with high spectral resolution at the C, N, O, and Al K-edges. In addition, we present the x-ray transmission of the dewar gate valve and of the filters mounted on the SXS filter wheel (external to the dewar), including beryllium, polyimide, and neutral density filters.

DOI： 10.1117/1.JATIS.4.2.021406

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer New York LLC  

The pulse shape processor is the onboard digital electronics unit of the X-ray microcalorimeter instrument—the soft X-ray spectrometer—onboard the Hitomi satellite. It processes X-ray events using the optimum filtering with limited resources. It was operated for 36 days in orbit continuously without issues and met the requirement of processing a (Formula presented.) event rate during the observation of bright sources. Here, we present the results obtained in orbit, focusing on its performance as the onboard digital signal processing unit of an X-ray microcalorimeter.

DOI： 10.1007/s10909-018-1861-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present results of inflight calibration of the point spread function of the Soft X-ray Telescope that focuses X-rays onto the pixel array of the Soft X-ray Spectrometer system. We make a full array image of a point-like source by extracting a pulsed component of the Crab nebula emission. Within the limited statistics afforded by an exposure time of only 6.9 ks and limited knowledge of the systematic uncertainties, we find that the raytracing model of 1.'2 half-power-diameter is consistent with an image of the observed event distributions across pixels. The ratio between the Crab pulsar image and the raytracing shows scatter from pixel to pixel that is 40% or less in all except one pixel. The pixel-to-pixel ratio has a spread of 20%, on average, for the 15 edge pixels, with an averaged statistical error of 17% (1 sigma). In the central 16 pixels, the corresponding ratio is 15% with an error of 6%.

DOI： 10.1093/pasj/psx146

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx138

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx127

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psy004

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx156

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx147

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx072

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Publishing type：Research paper (scientific journal)  

© The Author(s) 2017. Published by Oxford University Press on behalf of the Astronomical Society of Japan. To search for giant X-ray pulses correlated with the giant radio pulses (GRPs) from the Crab pulsar, we performed a simultaneous observation of the Crab pulsar with the X-ray satellite Hitomi in the 2-300 keV band and the Kashima NICT radio telescope in the 1.4-1.7 GHz band with a net exposure of about 2 ks on 2016 March 25, just before the loss of the Hitomi mission. The timing performance of the Hitomi instruments was confirmed to meet the timing requirement and about 1000 and 100 GRPs were simultaneously observed at the main pulse and inter-pulse phases, respectively, and we found no apparent correlation between the giant radio pulses and the X-ray emission in either the main pulse or inter-pulse phase. All variations are within the 2 σ fluctuations of the X-ray fluxes at the pulse peaks, and the 3 σ upper limits of variations of main pulse or inter-pulse GRPs are 22% or 80% of the peak flux in a 0.20 phase width, respectively, in the 2-300 keV band. The values for main pulse or inter-pulse GRPs become 25% or 110%, respectively, when the phase width is restricted to the 0.03 phase. Among the upper limits from the Hitomi satellite, those in the 4.5-10 keV and 70-300 keV bands are obtained for the first time, and those in other bands are consistent with previous reports. Numerically, the upper limits of the main pulse and inter-pulse GRPs in the 0.20 phase width are about (2.4 and 9.3) × 10−11 erg cm−2, respectively. No significant variability in pulse profiles implies that the GRPs originated from a local place within the magnetosphere. Although the number of photon-emitting particles should temporarily increase to account for the brightening of the radio emission, the results do not statistically rule out variations correlated with the GRPs, because the possible X-ray enhancement may appear due to a >0.02% brightening of the pulse-peak flux under such conditions.

DOI： 10.1093/pasj/psx083

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx151

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Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

DOI： 10.1093/pasj/psx154

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The X-Ray Spectrometer (XRS) instrument of Suzaku provided the first measurement of the non-X-ray background (NXB) of an X-ray calorimeter spectrometer, but the data set was limited. The Soft X-ray Spectrometer (SXS) instrument of Hitomi was able to provide a more detailed picture of X-ray calorimeter background, with more than 360 ks of data while pointed at the Earth, and a comparable amount of blank-sky data. These data are important not only for analyzing SXS science data, but also for categorizing the contributions to the NXB in X-ray calorimeters as a class. In this paper, we present the contributions to the SXS NXB, the types and effectiveness of the screening, the interaction of the screening with the broad-band redistribution, and the residual background spectrum as a function of magnetic cut-off rigidity. The orbit-averaged SXS NXB in the range 0.3-12 keV was 4 x 10(-2) counts s(-1) cm(-2). This very low background in combination with groundbreaking spectral resolution gave SXS unprecedented sensitivity to weak spectral lines.

DOI： 10.1093/pasj/psx139

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Publishing type：Research paper (scientific journal)  

We summarize results of the initial in-orbit performance of the pulse shape processor (PSP) of the soft x-ray spectrometer instrument onboard ASTRO-H (Hitomi). Event formats, kind of telemetry, and the pulse-processing parameters are described, and the parameter settings in orbit are listed. The PSP was powered-on 2 days after launch, and the event threshold was lowered in orbit. The PSP worked fine in orbit, and there was neither memory error nor SpaceWire communication error until the break-up of spacecraft. Time assignment, electrical crosstalk, and the event screening criteria are studied. It is confirmed that the event processing rate at 100% central processing unit load is ∼200 c / s / array, compliant with the requirement on the PSP.

DOI： 10.1117/1.JATIS.4.1.011217

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© 2018 SPIE. We are working on an updated program of the future Japanese X-ray satellite mission DIOS (Diffuse Intergalactic Oxygen Surveyor), called Super DIOS. We keep the main aim of searching for dark baryons in the form of warmhot intergalactic medium (WHIM) with high-resolution X-ray spectroscopy. The mission will detect redshifted emission lines from OVII, OVIII and other ions, leading to an overall understanding of the physical nature and spatial distribution of dark baryons as a function of cosmological timescale. We are working on the conceptual design of the satellite and onboard instruments, with a provisional launch time in the early 2030s. The major changes will be improved angular resolution of the X-ray telescope and increased number of TES calorimeter pixels. Super DIOS will have a 10-arcsecond resolution and a few tens of thousand TES pixels. Most contaminating X-ray sources will be resolved, and the level of diffuse X-ray background will be reduced after subtraction of point sources. This will give us very high sensitivity to map out the WHIM in emission. The status of the spacecraft study will be presented: the development plan of TES calorimeters, on-board cooling system, X- ray telescope, and the satellite system. The previous study results for DIOS and technical achievements reached by the Hitomi (ASTRO-H) mission provide baseline technology for Super DIOS. We will also consider large scale international collaboration for all the on-board instruments.

DOI： 10.1117/12.2313122

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

We summarize all of the in-orbit operations of the soft x-ray spectrometer (SXS) onboard the ASTRO-H (Hitomi) satellite. The satellite was launched on February 17, 2016, and the communication with the satellite ceased on March 26, 2016. The SXS was still in the commissioning phase, in which the set-ups were progressively changed. This paper is intended to serve as a concise reference of the events in orbit in order to properly interpret the SXS data taken during its short lifetime and as a test case for planning the in-orbit operation for future microcalorimeter missions.

DOI： 10.1117/1.JATIS.4.1.011205

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

The soft x-ray spectrometer (SXS) was a cryogenic high-resolution x-ray spectrometer onboard the Hitomi (ASTRO-H) satellite that achieved energy resolution of 5 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator (ADR). The cooling chain from room temperature to the ADR heat sink was composed of two-stage Stirling cryocoolers, a 4He Joule-Thomson cryocooler, and superfluid liquid helium and was installed in a dewar. It was designed to achieve a helium lifetime of more than 3 years with a minimum of 30 L. The satellite was launched on February 17, 2016, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the helium tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and the cryocoolers.

DOI： 10.1117/1.JATIS.4.1.011208

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Publishing type：Research paper (scientific journal)  

© The Authors 2018. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. The soft x-ray spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from microvibration from cryocoolers mounted on the dewar. This is mitigated for the flight model (FM) by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the FM was verified before launch of the spacecraft in both ambient condition and thermal-vacuum condition, showing no detectable degradation in energy resolution. The in-orbit detector spectral performance and cryocooler cooling performance were also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the microvibration could degrade the cryogenic detector is shown. Lessons learned from the development to mitigate unexpected issues are also described.

DOI： 10.1117/1.JATIS.4.1.011216

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

The soft x-ray spectrometer (SXS) instrument was launched aboard the Astro-H (Hitomi) observatory on February 17, 2016. The SXS is based on a high-sensitivity x-ray calorimeter detector system that has been successfully deployed in many ground and suborbital spectrometers. The instrument was to provide essential diagnostics for nearly every class of x-ray emitting objects from the atmosphere of Jupiter to the outskirts of galaxy clusters, without degradation for spatially extended objects. The SXS detector system consisted of a 36-pixel cryogenic microcalorimeter array operated at a heat sink temperature of 50 mK. In preflight testing, the detector system demonstrated a resolving power of better than 1300 at 6 keV with a simultaneous bandpass from below 0.3 keV to above 12 keV with a timing precision better than 100 μs. In addition, a solid-state anticoincidence detector was placed directly behind the detector array for background suppression. The detector error budget included the measured interference from the SXS cooling system and the spacecraft. Additional margin for on-orbit gain stability and on-orbit spacecraft interference were also included predicting an on-orbit performance that meets or exceeds the 7-eV FWHM at 6-keV requirement. The actual on-orbit spectral resolution was better than 5 eV FWHM at 6 keV, easily satisfying the instrument requirement. Here, we discuss the actual on-orbit performance of the SXS detector system and compare this to performance in preflight testing and the on-orbit predictions. We will also discuss the on-orbit gain stability, additional on-orbit interference, and measurements of the on-orbit background.

DOI： 10.1117/1.JATIS.4.1.011218

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPIE  

The soft x-ray spectrometer (SXS) instrument was launched aboard the Astro-H (Hitomi) observatory on February 17, 2016. The SXS is based on a high-sensitivity x-ray calorimeter detector system that has been successfully deployed in many ground and suborbital spectrometers. The instrument was to provide essential diagnostics for nearly every class of x-ray emitting objects from the atmosphere of Jupiter to the outskirts of galaxy clusters, without degradation for spatially extended objects. The SXS detector system consisted of a 36-pixel cryogenic microcalorimeter array operated at a heat sink temperature of 50 mK. In preflight testing, the detector system demonstrated a resolving power of better than 1300 at 6 keV with a simultaneous bandpass from below 0.3 keV to above 12 keV with a timing precision better than 100 μs. In addition, a solid-state anticoincidence detector was placed directly behind the detector array for background suppression. The detector error budget included the measured interference from the SXS cooling system and the spacecraft. Additional margin for on-orbit gain stability and on-orbit spacecraft interference were also included predicting an on-orbit performance that meets or exceeds the 7-eV FWHM at 6-keV requirement. The actual on-orbit spectral resolution was better than 5 eV FWHM at 6 keV, easily satisfying the instrument requirement. Here, we discuss the actual on-orbit performance of the SXS detector system and compare this to performance in preflight testing and the on-orbit predictions. We will also discuss the on-orbit gain stability, additional on-orbit interference, and measurements of the on-orbit background.

DOI： 10.1117/1.JATIS.4.1.011218

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The metal abundance of the hot plasma that permeates galaxy clusters represents the accumulation of heavy elements produced by billions of supernovae(1). Therefore, X-ray spectroscopy of the intracluster medium provides an opportunity to investigate the nature of supernova explosions integrated over cosmic time. In particular, the abundance of the iron-peak elements (chromium, manganese, iron and nickel) is key to understanding how the progenitors of typical type Ia supernovae evolve and explode(2-6). Recent X-ray studies of the intracluster medium found that the abundance ratios of these elements differ substantially from those seen in the Sun(7-11), suggesting differences between the nature of type Ia supernovae in the clusters and in the Milky Way. However, because the K-shell transition lines of chromium and manganese are weak and those of iron and nickel are very close in photon energy, highresolution spectroscopy is required for an accurate determination of the abundances of these elements. Here we report observations of the Perseus cluster, with statistically significant detections of the resonance emission from chromium, manganese and nickel. Our measurements, combined with the latest atomic models, reveal that these elements have near-solar abundance ratios with respect to iron, in contrast to previous claims. Comparison between our results and modern nucleosynthesis calculations(12-14) disfavours the hypothesis that type Ia supernova progenitors are exclusively white dwarfs with masses well below the Chandrasekhar limit (about 1.4 times the mass of the Sun). The observed abundance pattern of the iron-peak elements can be explained by taking into account a combination of near-and sub-Chandrasekhar-mass type Ia supernova systems, adding to the mounting evidence that both progenitor types make a substantial contribution to cosmic chemical enrichment(5,15,16).

DOI： 10.1038/nature24301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We propose a mechanism of state transition in wind-fed black hole (BH) binaries (high-mass X-ray binaries) such as Cyg X-1 and LMC X-1. Modeling a line-driven stellar wind from the companion by two-dimensional hydrodynamical calculations, we investigate the processes of wind capture by, and accretion onto, the BH. We assume that the wind acceleration is terminated at the He II ionization front because ions responsible for line-driven acceleration are ionized within the front, i.e., the He III region. It is found that the mass accretion rate inferred from the luminosity is remarkably smaller than the capture rate. Considering the difference, we construct a model for the state transition based on the accretion flow being controlled by magnetorotational instability. The outer flow is torus-like, and plays an important role to trigger the transition. The model can explain why state transition does occur in Cyg X-1, while not in LMC X-1. Cyg X-1 exhibits a relatively low luminosity, and then the He II ionization front is located and can move between the companion and BH, depending on its ionizing photon flux. On the other hand, LMC X-1 exhibits too high luminosity for the front to move considerably; the front is too close to the companion atmosphere. The model also predicts that each state of high-soft or low-hard would last fairly long because the luminosity depends weakly on the wind velocity. In the context of the model, the state transition is triggered by a fluctuation of the magnetic field when its amplitude becomes comparable to the field strength in the torus-like outer flow.

DOI： 10.3847/1538-4357/aa88d3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We show the softest ever spectrum from Cyg X-1, detected in 2013 with Suzaku. This has the weakest high-energy Compton tail ever seen from this object, so should give the cleanest view of the underlying disk spectrum, and hence the best determination of black hole spin from disk continuum fitting. Using the standard model of a disk with simple non-thermal Comptonization to produce the weak high-energy tail gives a highspin black hole. However, we get a significantly better fit by including an additional, low-temperature thermal Comptonization component, which allows a much lower black hole spin. Corroboration of the existence of an additional Compton component comes from the frequency-dependent hard lags seen in the rapid variability in archival high/soft state data. These cannot be explained if the continuum is a single non-thermal Comptonization component, but are instead consistent with a radially stratified, multi-zone Comptonization spectrum, where the spectrum is softer further from the black hole. A complex multi-zone Comptonization continuum is required to explain both spectra and timing together, and this has an impact on the derived black hole spin.

DOI： 10.1093/pasj/psx009

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified E approximate to 3.5 keV emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S XVI (E similar or equal to 3.44 keV rest-frame)-a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

DOI： 10.3847/2041-8213/aa61fa

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

One of the remarkable features of blazars is violent variability over a wide wavelength range. The variation mechanism causing the observed complex behavior is still under debate. The variability timescales range from less than a day to decades. Variation on timescales less than a day is known as "microvariability." Such short-term variations can provide insights regarding the origin of the variability after they are distinguished from longer-term variational components. We select about 195 microvariability events from the continuous light curve of blazar W2R 1926+42 with 1-min time resolution obtained by the Kepler spacecraft, and estimate the timescale and amplitude of each event. The rise and decay timescales of the events reveal random variations over short timescales less than a day, but they indicate systematic variations on timescales longer than several days. This result implies that the events are not independent, but rather mutually correlated.

DOI： 10.3390/galaxies5010013

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We analyze the Kepler monitoring light curve of a blazar W2R 1926+42 to examine features of microvariability by means of the "shot analysis" technique. We select 195 intra-day, flare-like variations (shots) for the continuous light curve of Quarter 14 with a duration of 100 d. In the application of the shot analysis, an averaged profile of variations is assumed to converge with a universal profile which reflects a physical mechanism generating themicrovariability in a blazar jet, although light-variation profiles of selected shots show a variety. A mean profile, which is obtained by aligning the peaks of the 195 shots, is composed of a spiky-shaped shot component at +/-0.1 d (with respect to the time of the peak), and two slow varying components ranging from -0.50 d to -0.15 d and from 0.10 d to 0.45 d of the peak time. The former spiky feature is well represented by an exponential rise of 0.043 +/- 0.001 d and an exponential decay of 0.061 +/- 0.002 d. These timescales are consistent with that corresponding to a break frequency of a power spectrum density calculated from the obtained light curve. After verification with the Monte Carlo method, the exponential shape, but not the observed asymmetry, of the shot component can be explained by noise variation. The asymmetry is difficult to explain through a geometrical effect (i.e., changes of the geometry of the emitting region), but is more likely to be caused by the production and dissipation of high-energy accelerated particles in the jet. Additionally, the durations of the detected shots show a systematic variation with a dispersion caused by a statistical randomness. A comparison with the variability of Cygnus X-1 is also briefly discussed.

DOI： 10.1093/pasj/psw119

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.72.2.0_495

CiNii Article

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.72.1.0_673

CiNii Article

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1109/TASC.2016.2646374

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

A detailed search for emission and absorption lines and an assessment of their upper limits are performed for Suzaku data. The method utilizes a matched-filtering approach to maximize the signal-to-noise ratio for a given energy resolution, which could be applicable to many types of line search. We first applied it to well-known active galactic nuclei spectra that have been reported to have ultra-fast outflows, and find that our results are consistent with previous findings at the similar to 3 sigma level. We proceeded to search for emission and absorption features in two bright magnetars 4U 0142+61 and 1RXS J1708-4009, applying the filtering method to Suzaku data. We found that neither source showed any significant indication of line features, even using long-term Suzaku observations or dividing their spectra into spin phases. The upper limits on the equivalent width of emission/absorption lines are constrained to be a few eV at similar to 1 keV and a few hundreds of eV at similar to 10 keV. This strengthens previous reports that persistently bright magnetars do not show proton cyclotron absorption features in soft X-rays and, even if they exist, they would be broadened or much weaker than below the detection limit of X-ray CCD.

DOI： 10.1093/pasj/psw091

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

From 2013 April to 2014 April, we performed X-ray and optical simultaneous monitoring of the type 1.5 Seyfert galaxy NGC 3516. We employed Suzaku and five Japanese ground-based telescopes - the Pirka, Kiso Schmidt, Nayuta, MITSuME, and the Kanata telescopes. The Suzaku observations were conducted seven times with various intervals ranging from days or weeks to months, with an exposure of ∼50 ks each. The optical B-band observations not only covered those of Suzaku almost simultaneously, but also followed the source as frequently as possible. As a result, NGC 3516 was found in its faint phase with a 2-10 keV flux of 0.21-2.70 �10-11 erg s-1 cm-2. The 2-45 keV X-ray spectra were composed of a dominant variable hard power-law (PL) continuum with a photon index of ∼1.7 and a non-relativistic reflection component with a prominent Fe-Kα emission line. Producing the B-band light curve by differential image photometry, we found that the B-band flux changed by ∼2.7 �10-11 erg s-1 cm-2, which is comparable to the X-ray variation, and we detected a significant flux correlation between the hard PL component in X-rays and the B-band radiation, for the first time in NGC 3516. By examining their correlation, we found that the X-ray flux preceded that in the B band by 2.0-0.6+0.07 days (1σ error). Although this result supports the X-ray reprocessing model, the derived lag is too large to be explained by the standard view, which assumes a "lamppost"-type X-ray illuminator located near a standard accretion disk. Our results are better explained by assuming a hot accretion flow and a truncated disk.

DOI： 10.3847/0004-637X/828/2/78

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS INC  

High-resolution pionic atom X-ray spectroscopy was performed with an X-ray spectrometer based on a 240 pixel array of superconducting transition-edge sensor (TES) microcalorimeters at the pi M1 beam line of the Paul Scherrer Institute. X-rays emitted by pionic carbon via the 4f -&gt; 3d transition and the parallel 4d -&gt; 3p transition were observed with a full width at half maximum energy resolution of 6.8 eV at 6.4 keV. The measured X-ray energies are consistent with calculated electromagnetic values which considered the strong interaction effect assessed via the Seki-Masutani potential for the 3p energy level, and favor the electronic population of two filled 1s electrons in the K-shell. Absolute energy calibration with an uncertainty of 0.1 eV was demonstrated under a high-rate hadron beam condition of 1.45 MHz. This is the first application of a TES spectrometer to hadronic atom X-ray spectroscopy and is an important milestone towards next-generation high-resolution kaonic atom X-ray spectroscopy.

DOI： 10.1093/ptep/ptw130

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

From 2013 April to 2014 April, we performed X-ray and optical simultaneous monitoring of the type 1.5 Seyfert galaxy NGC. 3516. We employed Suzaku and five Japanese ground-based telescopes-the Pirka, Kiso Schmidt, Nayuta, MITSuME, and the Kanata telescopes. The Suzaku observations were conducted seven times with various intervals ranging from days or weeks to months, with an exposure of similar to 50 ks each. The optical B-band observations not only covered those of Suzaku almost simultaneously, but also followed the source as frequently as possible. As a result, NGC. 3516 was found in its faint phase with a 2-10 keV flux of 0.21-2.70. x 10(-1)1 erg s(-1) cm(-2). The 2-45 keV X-ray spectra were composed of a dominant variable hard power-law (PL) continuum with a photon index of similar to 1.7 and a nonrelativistic reflection component with a prominent Fe-Ka emission line. Producing the B-band light curve by differential image photometry, we found that the B-band flux changed by similar to 2.7 x 10(-1)1 erg s(-1) cm(-2), which is comparable to the X-ray variation, and we detected a significant flux correlation between the hard PL component in X-rays and the B-band radiation, for the first time in NGC. 3516. By examining their correlation, we found that the X-ray flux preceded that in the B band by 2.0(-0.6)(+0.7) days (1 sigma error). Although this result supports the X-ray reprocessing model, the derived lag is too large to be explained by the standard view, which assumes a "lamppost"-type X-ray illuminator located near a standard accretion disk. Our results are better explained by assuming a hot accretion flow and a truncated disk.

DOI： 10.3847/0004-637X/828/2/78

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We present the latest update and progress on the future Japanese X-ray satellite mission Diffuse Intergalactic Oxygen Surveyor (DIOS). DIOS is proposed to JAXA as a small satellite mission, and would be launched with an Epsilon rocket. DIOS would carry on the legacy of ASTRO-H, which carries semiconductor-based microcalorimeters and is scheduled to be launched in 2016, in high-resolution X-ray spectroscopy. A 400-pixel array of transition-edge sensors (TESs) would be employed, so DIOS would also provide valuable lessons for the next ESA X-ray mission ATHENA on TES operation and cryogen-free cooling in space. We have been sophisticating the entire design of the satellite to meet the requirement for the Epsilon payload for the next call. The primary goal of the mission is to search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy by detecting redshifted emission lines from OVII and OVIII ions. The results would have significant impacts on our understanding of the nature of "dark baryons," their total amount and spatial distribution, as well as their evolution over cosmological timescales.

DOI： 10.1007/s10909-015-1362-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

A performance evaluation of superconducting transition-edge sensors (TESs) in the environment of a pion beam line at a particle accelerator is presented. Averaged across the 209 functioning sensors in the array, the achieved energy resolution is 5.2 eV FWHM at Co (6.9 keV) when the pion beam is off and 7.3 eV at a beam rate of 1.45 MHz. Absolute energy uncertainty of 0.04 eV is demonstrated for Fe (6.4 keV) with in-situ energy calibration obtained from other nearby known X-ray lines. To achieve this small uncertainty, it is essential to consider the non-Gaussian energy response of the TESs and thermal cross-talk pile-up effects due to charged particle hits in the silicon substrate of the TES array.

DOI： 10.1007/s10909-016-1491-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

Calorimetric X-ray detectors are very sensitive to their environment. The boundary conditions can have a profound effect on the gain including heat sink temperature, the local radiation temperature, bias, and the temperature of the readout electronics. Any variation in the boundary conditions can cause temporal variations in the gain of the detector and compromise both the energy scale and the resolving power of the spectrometer. Most production X-ray calorimeter spectrometers, both on the ground and in space, have some means of tracking the gain as a function of time, often using a calibration spectral line. For small gain changes, a linear stretch correction is often sufficient. However, the detectors are intrinsically non-linear and often the event analysis, i.e., shaping, optimal filters etc., add additional non-linearity. Thus for large gain variations or when the best possible precision is required, a linear stretch correction is not sufficient. Here, we discuss a new correction technique based on non-linear interpolation of the energy-scale functions. Using Astro-H/SXS calibration data, we demonstrate that the correction can recover the X-ray energy to better than 1 part in 10 over the entire spectral band to above 12 keV even for large-scale gain variations. This method will be used to correct any temporal drift of the on-orbit per-pixel gain using on-board calibration sources for the SXS instrument on the Astro-H observatory.

DOI： 10.1007/s10909-016-1503-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We are developing a transition edge sensor (TES) using multilayer readout wiring for future X-ray astronomy satellites. Although we fabricated a first full 2020 pixels TES array, we could not confirm transition of the TES. Considering possible causes, we focused on surface roughness of the TES film. We checked the fabrication process steps that can influence the surface roughness step by step, and changed wiring material (Al to Nb) and also a process condition of an ion milling. As a result, we succeeded to reduce the surface roughness from 4.5 to 2.5 nm rms at 1 m scale. However, the transition was not observed probably because the TES films in our samples with surface roughness more than nm rms tend not to show the transition. Therefore, to suppress the surface roughness even more, we discuss possible process effects and mitigations.

DOI： 10.1007/s10909-016-1499-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Clusters of galaxies are the most massive gravitationally bound objects in the Universe and are still forming. They are thus important probes(1) of cosmological parameters and many astrophysical processes. However, knowledge of the dynamics of the pervasive hot gas, the mass of which is much larger than the combined mass of all the stars in the cluster, is lacking. Such knowledge would enable insights into the injection of mechanical energy by the central supermassive black hole and the use of hydrostatic equilibrium for determining cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50-million-kelvin diffuse hot plasma filling its gravitational potential well. The active galactic nucleus of the central galaxy NGC 1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These bubbles probably induce motions in the intracluster medium and heat the inner gas, preventing runaway radiative cooling-a process known as active galactic nucleus feedback(2-6). Here we report X-ray observations of the core of the Perseus cluster, which reveal a remarkably quiescent atmosphere in which the gas has a line-of-sight velocity dispersion of 164 +/- 10 kilometres per second in the region 30-60 kiloparsecs from the central nucleus. A gradient in the line-of-sight velocity of 150 +/- 70 kilometres per second is found across the 60-kiloparsec image of the cluster core. Turbulent pressure support in the gas is four per cent of the thermodynamic pressure, with large-scale shear at most doubling this estimate. We infer that a total cluster mass determined from hydrostatic equilibrium in a central region would require little correction for turbulent pressure.

DOI： 10.1038/nature18627

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Utilizing archived Suzaku data acquired on 2007 December 25 for 46 ks, the X-ray spectroscopic properties of the dipping and eclipsing low-mass X-ray binary EXO 0748-676 were studied. At an assumed distance of 7.1 kpc, the data provided a persistent unabsorbed luminosity of 3.4 x 10(36) erg cm(-2) s(-1) in 0.6-55 keV. The source was in a relatively bright low/hard state, wherein the 0.6-55 keV spectrum can be successfully explained by a "double-seed" Comptonization model incorporating a common corona with an electron temperature of similar to 13 keV. The seed photons are thought to be supplied from both the neutron star surface and a cooler truncated disk. Compared to a sample of non-dipping, low-mass X-ray binaries in the low/hard state, the spectrum is subject to stronger Comptonization with a relatively larger Comptonizing y-parameter of similar to 1.4 and a larger coronal optical depth of similar to 5. This result, when attributed to the high inclination of EXO 0748-676, suggests that the Comptonizing corona may elongate along the disk plane and provide a longer path for the seed photons when viewed from edge-on inclinations.

DOI： 10.3847/0004-637X/823/2/131

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The bright and highly variable Seyfert I active galactic nucleus IC 4329A was observed with Suzaku five times in 2007 August, with intervals of similar to 5 days and a net exposure of 24-31 ks each. Another longer observation was carried out in 2012 August with a net exposure of 118 ks. In the six observations, a source was detected in 2-45 keV with an average 2-10 keV fluxes of (0.67-1.2) x 10(-10) erg cm(-2) s(-1). Its intensity changed by a factor of 2 among the five observations in 2007, and 1.5 within the 2012 observation. A difference of spectrum among these observations revealed that the variability of IC4329A was carried mainly by a power-law component with a photon index Gamma similar to 2.0. However, in addition to this primary component and its associated reflection, the broad-band Suzaku data required another, harder, and less-variable component with Gamma similar to 1.4. The presence of this new continuum was also confirmed by analyzing the same six data sets through the spectral decomposition technique developed by Noda et al. (2013a, ApJ, 771, 100). This Gamma similar to 1.4 continuum is considered to be a new primary component that has not been recognized in the spectra of IC 4329A so far, although it was recently identified in those of several other Seyfert I galaxies (Noda et al. 2013a, ApJ, 771, 100; Noda et al. 2014, ApJ, 794, 2).

DOI： 10.1093/pasj/psw025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We visually inspected the light curves of 7557 Kepler Objects of Interest (KOIs) to search for single. transit events (STEs) that were possibly due to long-period giant planets. We identified 28 STEs in 24 KOIs, among which 14 events are newly reported in this paper. We estimate the radius and orbital period of the objects causing STEs by fitting the STE light curves simultaneously with the transits of the other planets in the system or with. prior information on the host star density. As a result, we found that STEs in seven of those systems are consistent with Neptune- to Jupiter-sized objects of orbital periods ranging from a few to similar to 20 years. We also estimate that. greater than or similar to 20% of the compact multi-transiting systems host cool giant planets with periods greater than or similar to 3 years on the basis of their occurrence in the KOIs with multiple candidates, assuming the small mutual inclination between inner and outer planetary orbits.

DOI： 10.3847/0004-637X/822/1/2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

Thunderclouds can produce bremsstrahlung gamma-ray emission, and sometimes even positrons. At 00:27:00 (UT) on 13 January 2012, an intense burst of gamma rays from a thundercloud was detected by the GROWTH experiment, located in Japan, facing the Sea of Japan. The event started with a sharp gamma-ray flash with a duration of &lt
300 ms coincident with an intracloud discharge, followed by a decaying longer gamma-ray emission lasting for ∼60 s. The spectrum of this prolonged emission reached ∼10 MeV, and contained a distinct line emission at 508±3(stat.)±5(sys.) keV, to be identified with an electron-positron annihilation line. The line was narrow within the instrumental energy resolution (∼80keV), and contained 520±50 photons which amounted to ∼10% of the total signal photons of 5340±190 detected over 0.1-10 MeV. As a result, the line equivalent width reached 280±40 keV, which implies a nontrivial result. The result suggests that a downward positron beam produced both the continuum and the line photons.

DOI： 10.1103/PhysRevE.93.021201

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Other Link： http://orcid.org/0000-0003-3529-3029

Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_509

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.71.2.0_367

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

We summarize results of the initial in-orbit performance of the pulse shape processor (PSP) of the soft x-ray spectrometer instrument onboard ASTRO-H (Hitomi). Event formats, kind of telemetry, and the pulse processing parameters are described, and the parameter settings in orbit are listed. PSP was powered-on two days after launch, and the event threshold was lowered in orbit. PSP worked fine in orbit, and there were no memory error nor SpaceWire communication error until the break-up of spacecraft. Time assignment, electrical crosstalk, and the event screening criteria are studied. It is confirmed that the event processing rate at 100% CPU load is similar to 200 c/s/array, compliant with the requirement on PSP.

DOI： 10.1117/12.2234222

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The SXS instrument was launched aboard the Astro-H observatory on February 17, 2016. The SXS spectrometer is based on a high sensitivity x-ray calorimeter detector system that has been successfully deployed in many ground and sub-orbital spectrometers. The instrument was to provide essential diagnostics for nearly every class of x-ray emitting objects from the atmosphere of Jupiter to the outskirts of galaxy clusters, without degradation for spatially extended objects. The SXS detector system consisted of a 36-pixel cryogenic microcalorimeter array operated at a heat sink temperature of 50 mK. In pre-flight testing, the detector system demonstrated a resolving power of better than 1300 at 6 keV with a simultaneous band-pass from below 0.3 keV to above 12 keV with a timing precision better than 100 mu s. In addition, a solid-state anti-coincidence detector was placed directly behind the detector array for background suppression. The detector error budget included the measured interference from the SXS cooling system and the spacecraft. Additional margin for on-orbit gain-stability, and on-orbit spacecraft interference were also included predicting an on-orbit performance that meets or exceeds the 7 eV FWHM at 6 keV requirement. The actual on-orbit spectral resolution was better than 5 eV FWHM at 6 keV, easily satisfying the instrument requirement. Here we discuss the actual on-orbit performance of the SXS detector system and compare this to performance in pre-flight testing and the on-orbit predictions. We will also discuss the on-orbit gain stability, additional on-orbit interference, and measurements of the on-orbit background.

DOI： 10.1117/12.2232799

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_735

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

Soft X-ray Spectrometer (SXS) onboard ASTRO-H (named Hitomi after launch) is a microcalorimeter-type spectrometer, installed in a dewar to be cooled at 50 mK. The energy resolution of the SXS engineering model suffered from micro-vibration from cryocoolers mounted on the dewar. This is mitigated for the flight model by introducing vibration isolation systems between the cryocoolers and the dewar. The detector performance of the flight model was verified before launch of the spacecraft in both ambient condition and thermal-vac condition, showing no detectable degradation in energy resolution. The in-orbit performance was also consistent with that on ground, indicating that the cryocoolers were not damaged by launch environment. The design and performance of the vibration isolation system along with the mechanism of how the micro-vibration could degrade the cryogenic detector is shown.

DOI： 10.1117/12.2231832

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Publishing type：Research paper (scientific journal)  

DOI： 10.1063/1.4961075

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The Soft X-ray Spectrometer (SXS) is a cryogenic high-resolution X-ray spectrometer onboard the ASTRO-H satellite, that achieves energy resolution better than 7 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator. The cooling chain from room temperature to the ADR heat sink is composed of 2-stage Stirling cryocoolers, a He-4 Joule-Thomson cryocooler, and superfluid liquid He, and is installed in a dewar. It is designed to achieve a helium lifetime of more than 3 years with a minimum of 30 liters. The satellite was launched on 2016 February 17, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the He tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and cryocoolers.

DOI： 10.1117/12.2232933

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Publishing type：Research paper (international conference proceedings)  

© 2016 SPIE. The Hitomi (ASTRO-H) mission is the sixth Japanese X-ray astronomy satellite developed by a large international collaboration, including Japan, USA, Canada, and Europe. The mission aimed to provide the highest energy resolution ever achieved at E > 2 keV, using a microcalorimeter instrument, and to cover a wide energy range spanning four decades in energy from soft X-rays to gamma-rays. After a successful launch on 2016 February 17, the spacecraft lost its function on 2016 March 26, but the commissioning phase for about a month provided valuable information on the on-board instruments and the spacecraft system, including astrophysical results obtained from first light observations. The paper describes the Hitomi (ASTRO-H) mission, its capabilities, the initial operation, and the instruments/spacecraft performances confirmed during the commissioning operations for about a month.

DOI： 10.1117/12.2232379

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We summarize all the in-orbit operations of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H (Hitomi) satellite. The satellite was launched on 2016/02/17 and the communication with the satellite ceased on 2016/03/26. The SXS was still in the commissioning phase, in which the setups were progressively changed. This article is intended to serve as a reference of the events in the orbit to properly interpret the SXS data taken during its short life time, and as a test case for planning the in-orbit operation for future micro-calorimeter missions.

DOI： 10.1117/12.2231784

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.

DOI： 10.1117/12.2232509

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The Soft X-ray Spectrometer (SXS) onboard the Astro-H (Hitomi) orbiting x-ray observatory featured an array of 36 silicon thermistor x-ray calorimeters optimized to perform high spectral resolution x-ray imaging spectroscopy of astrophysical sources in the 0.3-12 keV band. Extensive pre-flight calibration measurements are the basis for our modeling of the pulse-height-energy relation and energy resolution for each pixel and event grade, telescope collecting area, detector efficiency, and pulse arrival time.
Because of the early termination of mission operations, we needed to extract the maximum information from observations performed only days into the mission when the onboard calibration sources had not yet been commissioned and the dewar was still coming into thermal equilibrium, so our technique for reconstructing the per-pixel time-dependent pulse-height-energy relation had to be modified. The gain scale was reconstructed using a combination of an absolute energy scale calibration at a single time using a fiducial from an onboard radioactive source, and calibration of a dominant time-dependent gain drift component using a dedicated calibration pixel, as well as a residual time-dependent variation using spectra from the Perseus cluster of galaxies.
The energy resolution was also measured using the onboard radioactive sources. It is consistent with instrument-level measurements accounting for the modest increase in noise due to spacecraft systems interference. We use observations of two pulsars to validate our models of the telescope area and detector efficiency, and to derive a more accurate value for the thickness of the gate valve Be window, which had not been opened by the time mission operations ceased. We use observations of the Crab pulsar to refine the pixel-to-pixel timing and validate the absolute timing.

DOI： 10.1117/12.2234230

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

We are developing transition edge sensor (TES) arrays using multilayer superconducting readout wiring for future X-ray astronomical missions. The TES pixels are formed on the multilayer readout wiring composed of hot and return wires sandwiching an insulation layer. The interface between the wiring and the TES is formed by patterning the topmost wiring layer followed by deposition of the TES layer. To mitigate problems found in a past device, edges of the upper readout wiring are tapered with an ion milling method to enhance an electrical contact between the TES film and the upper readout wiring. To verify this design, we fabricated a 400-pixel test array with the TES pixels on the tapered upper readout wiring. Good physical contact between the TES film and the readout wiring was confirmed with scanning electron microscope. Furthermore, a low transition temperature (~160 mK), a sharp transition edge and a low residual resistance (~1 mΩ) were observed in RT measurements of representative pixels. The critical current was small 10 ~ 30 μA, although it is still larger than the previous device (&lt
10 μA). These results suggest that this method will enable a multilayer wiring TES array with good electrical properties.

DOI： 10.1109/TASC.2014.2374415

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

This paper reports the results of Suzaku observation of the spectral variation of the black hole binary LMCX-1 in the soft state. The observation was carried out in 2009 from July 21 to 24. the obtained net count rate was similar to 30 counts s(-1) in the 0.5-50 keV band with similar to 10% peak-to-peak flux variation. The time-averaged X-ray spectrum cannot be described by a multi-color disk and single Compton component with its reflection, but requires additional Comptonized emissions. This double Compton component model allows a slightly larger inner radius of the multi-color disk, implying a lower spin parameter. Significant spectral evolution was observed above 8 keV along with a flux decrease on a timescale of similar to 10(4)-10(5) s. By spectral fitting, we show that this behavior is well explained by changes in the hard Comptonized emission component in contrast to the maintained disk and soft Comptonized emission.

DOI： 10.1093/pasj/psv017

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present X-ray observations of the active galactic nucleus (AGN) in NGC 4785. The source is a local Seyfert 2 which has not been studied so far in much detail. It was recently detected with high significance in the 15-60 keV band in the 66-month Swift/BAT (Burst Array Telescope) all sky survey, but there have been no prior pointed X-ray observations of this object. With Suzaku, we clearly detect the source below 10 keV, and find it to have a flat continuum and prominent neutral iron fluorescence line with equivalent width greater than or similar to 1 keV. Fitting the broad-band spectra with physical reflection models shows the source to be a Compton-thick AGN with N-H of at least 2 x 10(24) cm(-2) and absorption-corrected 2-10 keV X-ray power L2-10 similar to few times 10(42) erg s(-1). Realistic uncertainties on L2-10 computed from the joint confidence interval on the intrinsic power-law continuum photon index and normalization are at least a factor of 10. The local bona fide Compton-thick AGN population is highly heterogeneous in terms of WISE mid-infrared source colours, and the nucleus of NGC 4785 appears especially sub-dominant in the mid-infrared when comparing to other Compton-thick AGN. Such sources would not be easily found using mid-infrared selection alone. The extent of host galaxy extinction to the nucleus is not clear, though NGC 4785 shows a complex core with a double bar and inner disc, adding to the list of known Compton-thick AGN in barred host galaxies.

DOI： 10.1093/mnras/stv344

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.1.0_471

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Publishing type：Research paper (scientific journal)  

© The Author 2014. We report MAXI and Swift observations of short-term spectral softenings of the Galactic black hole X-ray binary Swift J1753.5-0127 in the low/hard state. These softening events are characterized by a simultaneous increase of soft X-rays (2-4 keV) and a decrease of hard X-rays (15-50 keV) lasting for a few tens of days. The X-ray energy spectra during the softening periods can be reproduced with a model consisting of a multi-color disk blackbody and its Comptonized component. The fraction of the Comptonized component decreased from 0.30 to 0.15 when the spectrum became softer; meanwhile the inner disk temperature (Tin) increased from 0.2 to 0.45 keV. These results imply that the softening events are triggered by a short-term increase of the mass accretion rate. During the observed spectral softening events, the disk flux (Fdisk) and Tin did not obey the Fdisk ∝ (Tin )4 relation, suggesting that the inner disk radius does not reach the innermost stable circular orbit.

DOI： 10.1093/pasj/psu140

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The type I Seyfert galaxy NGC 3227 was observed by Suzaku six times in 2008, with intervals of similar to 1 week and net exposures of similar to 50 ks each. Among the six observations, the source varied by nearly an order of magnitude; it was brightest in the first observation with a 2-10 keV luminosity of 1.2 x 10(42) erg s(-1), while faintest in the fourth observation with 2.9 x 10(41) erg s(-1). As it became fainter, the continuum in the 2-45 keV band became harder, while the narrow Fe-Ka emission line, detected on all occasions at 6.4 keV of the source rest frame, remained approximately constant in the photon flux. Through a method of variability-assisted broadband spectroscopy, the 2-45 keV spectrum of NGC 3227 was decomposed into three distinct components. One is a relatively soft powerlaw continuum with a photon index of similar to 2.3, weakly absorbed and highly variable on timescales of similar to 5 ks; it was observed only when the source was above a threshold luminosity of similar to 6.6 x 10(41) erg s(-1) (in 2-10 keV), and was responsible for further source brightening beyond. Another is a harder and more absorbed continuum with a photon index of similar to 1.6, which persisted through the six observations and varied slowly on timescales of a few weeks by a factor of similar to 2. This component, carrying a major fraction of the broadband emission when the source is below the threshold luminosity, is considered as an additional primary emission. The last one is a reflection component with the narrow iron line, produced at large distances from the central black hole.

DOI： 10.1088/0004-637X/794/1/2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We are preparing for an ultra-high resolution X-ray spectroscopy of kaonic atoms using an X-ray spectrometer based on an array of superconducting transition-edge-sensor microcalorimeters developed by NIST. The instrument has excellent energy resolutions of 2-3 eV (FWHM) at 6 keV and a large collecting area of about 20 mm. This will open new door to investigate kaon-nucleus strong interaction and provide new accurate charged-kaon mass value.

DOI： 10.1007/s10909-014-1137-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We have developed Ti/Au bilayer transition-edge sensor (TES) microcalorimeters for future X-ray astrophysical satellite missions such as DIOS. One possible concern on the space use of TES microcalorimeters is its radiation tolerance. We have evaluated the performance of a Ti/Au bilayer (30/40 nm thick) TES microcalorimeter with 1.5 m thick Au absorber, before and after irradiation of 150 MeV proton beam with a total dose of 10 krad, corresponding to 10 years in the low Earth orbit. No significant changes on transition temperature, sensitivity, normal resistance, and critical current were observed. The energy resolution for 5.9 keV X-rays was 5.6 0.3 eV (FWHM) after the irradiation, which was slightly worse than 5.1 0.3 eV before the irradiation. We consider that our TES has sufficient radiation tolerance in orbit.

DOI： 10.1007/s10909-013-1058-4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We have fabricated multilayer readout wiring transition edge sensors (TES), which enable us to realize both large effective area and high-energy resolution for future X-ray astrophysical missions, such as diffuse intergalactic oxygen surveyor. By sandwiching a SiO insulation layer between Al superconducting signal and return lines, self/mutual inductances and self fielding of bias leads are expected to be reduced. We fabricated and TES array on the multilayer wiring and tested their performance. Under the low temperature condition, several pixels in the TES array showed sharp superconducting transitions at around 300 mK. We also succeeded in detecting X-ray signals from the TES, contrary to the previous results of TES. We further investigated the reasons for the differences between the TES and the TES, and present future plans for improving the multilayer TES array fabrication.

DOI： 10.1007/s10909-013-1056-6

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report on the results from Suzaku observations of the Galactic black hole X-ray binary H1743-322 in the low/hard state during its outburst in 2012 October. We appropriately take into account the effects of dust scattering to accurately analyze the X-ray spectra. The time-averaged spectra in the 1-200 keV band are dominated by a hard power-law component of a photon index of approximate to 1.6 with a high-energy cutoff at approximate to 60 keV, which is well described with the Comptonization of the disk emission by the hot corona. We estimate the inner disk radius from the multi-color disk component, and find that it is 1.3-2.3 times larger than the radius in the high/soft state. This suggests that the standard disk was not extended to the innermost stable circular orbit. A reflection component from the disk is detected with R = Omega/2 pi approximate to 0.6 (Omega is the solid angle). We also successfully estimate the stable disk component independent of the time-averaged spectral modeling by analyzing short-term spectral variability on a similar to 1 s timescale. A weak low-frequency quasi-periodic oscillation at 0.1-0.2 Hz is detected, whose frequency is found to correlate with the X-ray luminosity and photon index. This result may be explained by the evolution of the disk truncation radius.

DOI： 10.1088/0004-637X/789/2/100

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The symbiotic X-ray binary (SyXB) 4U 1954+ 319 is a rare system hosting a peculiar neutron star (NS) and an M-type optical companion. Its similar to 5.4 hr NS spin period is the longest among all known accretion-powered pulsars and exhibited large (similar to 7%) fluctuations over 8 yr. A spin trend transition was detected with Swift/BAT around an X-ray brightening in 2012. The source was in quiescent and bright states before and after this outburst based on 60 ks Suzaku observations in 2011 and 2012. The observed continuum is well described by a Comptonized model with the addition of a narrow 6.4 keV Fe-K alpha line during the outburst. Spectral similarities to slowly rotating pulsars in high-mass X-ray binaries, its high pulsed fraction (similar to 60%-80%), and the location in the Corbet diagram favor high B-field (greater than or similar to 10(12) G) over a weak field as in low-mass X-ray binaries. The observed low X-ray luminosity (10(33)-10(35) erg s(-1)), probable wide orbit, and a slow stellar wind of this SyXB make quasi-spherical accretion in the subsonic settling regime a plausible model. Assuming a similar to 10(13) G NS, this scheme can explain the similar to 5.4 hr equilibrium rotation without employing the magnetar-like field (similar to 10(16) G) required in the disk accretion case. The timescales of multiple irregular flares (similar to 50 s) can also be attributed to the free-fall time from the Alfven shell for a similar to 10(13) G field. A physical interpretation of SyXBs beyond the canonical binary classifications is discussed.

DOI： 10.1088/0004-637X/786/2/127

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Hercules X-1 was observed with Suzaku in the main-on state from 2005 to 2010. The 0.4-100 keV wide-band spectra obtained in four observations showed a broad hump around 4-9 keV in addition to narrow Fe lines at 6.4 and 6.7 keV. The hump was seen in all the four observations regardless of the selection of the continuum models. Thus it is considered a stable and intrinsic spectral feature in Her X-1. The broad hump lacked a sharp structure like an absorption edge. Thus it was represented by two different spectral models: an ionized partial covering or an additional broad line at 6.5 keV. The former required a persistently existing ionized absorber, whose origin was unclear. In the latter case, the Gaussian fitting of the 6.5-keV line needs a large width of sigma = 1.0-1.5 keV and a large equivalent width of 400-900 eV. If the broad line originates from Fe fluorescence of accreting matter, its large width may be explained by the Doppler broadening in the accretion flow. However, the large equivalent width may be inconsistent with a simple accretion geometry.

DOI： 10.1093/pasj/psu005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The neutron-star low-mass X-ray binary Aquila X-1 was observed by Suzaku seven times, from 2007 September 28 to October 30. The observations successfully traced an outburst decay in which the source luminosity decreased almost monotonically from similar to 10(37) erg s(-1) to similar to 10(34) erg s(-1), by similar to 3 orders of magnitude. To investigate luminosity-dependent changes in the accretion geometry, five of the seven data sets with a typical exposure of similar to 18 ks each were analyzed; the other two were utilized in a previous work (Sakurai et al. 2012, PASJ, 64, 72). The source was detected up to 100 keV in the second to the fourth observations, to 40 keV in the fifth, and to 10 keV on the last two occasions. All spectra were reproduced successfully by a Comptonized blackbody model with relatively high (greater than or similar to 2.0) optical depths, plus an additional softer optically-thick component. The faintest three spectra were reproduced alternatively by a single Comptonized blackbody model with a relatively low (less than or similar to 0.8) optical depth. The estimated radius of the blackbody emission, including seed photons for the Comptonization, was 10 +/- 2 km at a 0.8-100 keV luminosity of 2.4 x 10(36) erg s(-1) (the second to the fourth observations). In contrast, it decreased to 7 +/- 1 km and further to 3 +/- 1 km, at a luminosity of (4.8-5.2) x 10(35) erg s(-1) (the fifth observation) and similar to 2 x 10(34) erg s(-1) (the sixth and seventh), respectively, regardless of the above model ambiguity. This can be taken as evidence for the emergence of a weak magnetosphere from the neutron star.

DOI： 10.1093/pasj/pst010

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We present a systematic investigation of the gain properties of a gas electron multiplier (GEM) foil in pure dimethyl ether (DME) at low pressures. The GEM is made from copper-clad liquid crystal polymer insulator (LCP-GEM) designed for space use, and is applied to a time projection chamber filled with low-pressure DME gas to observe the linear polarization of cosmic X-rays. We have measured gains of a 100 μm-thick LCP-GEM as a function of the voltage between GEM electrodes at various gas pressures ranging from 10 to 190 Torr with 6.4 keV X-rays. The highest gain at 190 Torr is about 2 × 104, while that at 20 Torr is about 500. We find that the pressure and electric-field dependence of the GEM gain is described by the first Townsend coefficient. The energy scale from 4.5 to 8.0 keV is linear with non-linearity of less than 1.4% above 30 Torr. © 2014 IOP Publishing Ltd and Sissa Medialab srl.

DOI： 10.1088/1748-0221/9/01/C01002

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2020 with JAXA's Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a very wide field of view (30-50 arcmin diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth's magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. We also consider revising the payload design to optimize the scientific capability allowed by the boundary conditions of the small mission.

DOI： 10.1117/12.2055731

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2020 with JAXA™s Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a very wide field of view (30-50 arcmin diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth™s magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. We also consider revising the payload design to optimize the scientific capability allowed by the boundary conditions of the small mission.

DOI： 10.1117/12.2055731

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We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of &lt
7eV in the energy range of 0.3 - 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.

DOI： 10.1117/12.2057199

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

Unified X-ray spectral and timing studies of Cygnus X-1 in the low/hard and hard intermediate state were conducted in a model-independent manner, using broadband Suzaku data acquired on 25 occasions from 2005 to 2009 with a total exposure of ̃450 ks. The unabsorbed 0.1-500 keV source luminosity changed over 0.8%-2.8% of the Eddington limit for 14.8 solar masses. Variations on short (1-2 seconds) and long (days to months) time scales require at least three separate components: a constant component localized below ̃2 keV, a broad soft one dominating in the 2-10 keV range, and a hard one mostly seen in the 10-300 keV range. In view of the truncated disk/hot inner-flow picture, these are respectively interpreted as emission from the truncated cool disk, a soft Compton component, and a hard Compton component. Long-term spectral evolution can be produced by the constant disk increasing in temperature and luminosity as the truncation radius decreases. The soft Compton component likewise increases, but the hard Compton does not, so that the spectrum in the hard intermediate state is dominated by the soft Compton component
on the other hand, the hard Compton component dominates the spectrum in the dim low/hard state, probably associated with a variable soft emission providing seed photons for the Comptonization. © 2013. Astronomical Society of Japan.

DOI： 10.1093/pasj/65.4.80

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We present the discovery of a reflection-dominated active galactic nucleus (AGN) in the early-type radio-quiet galaxy ESO 565-G019 with Suzaku and Swift/Burst Alert Telescope. The source X-ray spectrum below 10 keV is characteristic of other Compton-thick (CT) AGNs, clearly showing an inverted continuum and prodigious fluorescence iron emission above similar to 3 keV. A Compton shoulder to the neutral Fe K alpha line also appears to be present. There is evidence for long-term hard X-ray flux variability that we associate with changes in the intrinsic AGN power law. More of such reflection-dominated AGNs should be uncovered in the near future with the increased sensitivity of ongoing and new hard X-ray surveys. ESO 565-G019 is hosted in an early-type galaxy whose morphology has been variously classified as either type E or type S0. Only about 20 bona fide CT-AGNs have been identified in the local universe so far, and all exist in host galaxies with late Hubble types (S0 or later). CT columns of nuclear obscuring gas are uncommon in early-type galaxies in the local universe, so confirmation of the exact morphological class of ESO 565-G019 is important. Infrared photometry also shows the presence of large quantities of cool dust in the host, indicative of significant ongoing star formation. ESO 565-G019 may be the first identified local example of minor-merger-driven CT-AGN growth in an early-type host, or may be the result of interaction with its neighboring galaxy ESO 565-G018 in a wide pair.

DOI： 10.1088/0004-637X/773/1/51

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The Crab Nebula is one of the brightest and most stable sources in the X-ray sky. Year-scale flux variation from the object was recently revealed in the hard X-ray band by four satellites. This marked the first detection of year-scale variability from pulsar wind nebulae in the hard X-ray band. The Crab Nebula has been observed at least once a year for calibration purposes with the Suzaku Hard X-ray Detector (HXD) since its launch in 2005. In order to investigate possible spectral changes as well as flux variation, archival data of the HXD were analyzed. The flux variation reported by other instruments was confirmed in the 25-100 keV band by the HXD at a few percent level, but flux above 100 keV did not follow the trend in variation below 100 keV. The hardness ratios produced utilizing the PIN and GSO sensors installed in the HXD exhibit significant scattering, thereby indicating spectral variations in the hard X-ray band. The spectral changes were quantified by spectral fitting with a broken power-law model. The difference between the two photon indexes of the broken power-law model in harder and softer energy bands is in the range of &lt; 2.54. Taking into account a flux variation of 6.3% and a spectral variation time-scale of a few days, multi components of the broken power-law-shaped synchrotron emission with different cooling times are suggested.

DOI： 10.1093/pasj/65.4.74

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The bright type I Seyfert galaxy NGC 3516 was observed by Suzaku twice, in 2005 October 12-15 and 2009 October 28-November 2, for a gross time coverage of 242 and 544 ks and a net exposure of 134 and 255 ks, respectively. The 2-10 keV luminosity was 2.8x10(41) erg s(-1) in 2005 and 1.6x10(41) erg s(-1) in 2009. The 1.4-1.7 keV and 1.7-10 keV count rates both exhibited peak-to-peak variations of a factor of similar to 2 in 2005 and similar to 4 in 2009. In both observations, the 15-45 keV count rate was less variable. The 2-10 keV spectrum in 2005 was significantly more convex than that in 2009. Through a count-count plot technique, the 2-45 keV signals in both sets of data were successfully decomposed in a model-independent way into two distinct broadband components. One is a variable emission with a featureless spectral shape, and the other is a non-varying hard component accompanied by a prominent Fe-K emission line at 6.33 keV (6.40 keV in the rest frame). The former was successfully fitted by an absorbed power-law model, while the latter requires a new hard continuum in addition to a reflection component from distant materials. The spectral and variability differences between the two observations are mainly attributed to long-term changes of this new hard continuum, which was stable on timescales of several hundreds of kiloseconds.

DOI： 10.1088/0004-637X/771/2/100

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We report the first observation of 3-30 MeV prolonged gamma-ray emission that was abruptly terminated by lightning. The gamma-ray detection was made during winter thunderstorms on December 30, 2010, by the Gamma-Ray Observation of Winter Thunderclouds experiment carried out in a coastal area along the Sea of Japan. The gamma-ray flux lasted for less than 3 min, continuously hardening closer to the lightning occurrence. The hardening at energies of 3-10 MeV energies was most prominent. The gamma-ray flux abruptly ceased less than 800 ms before the lightning flash that occurred over 5 km away from the experimental site. In addition, we observed a clear difference in the duration of the 3-10 MeV gamma rays and those &gt
10 MeV, suggesting that the area of &gt
10 MeV gamma-ray emission is considerably smaller than that of the lower-energy gamma rays. This work may give a manifestation that a local region emitting prolonged gamma rays connects with a distant region to initiate lightning. © 2013 American Physical Society.

DOI： 10.1103/PhysRevLett.111.015001

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We present broadband X-ray analyses of the magnetar 1E 1547.0-5408 observed with Suzaku on 2010 August 7, nearly one and a half years after an intense outburst in 2009 January. The 2-10 keV flux decreased to (1.06 +/- 0.01) x 10(-11) erg cm(-2) s(-1), while the hard X-ray detection was 3.5 sigma (18-40 keV) and 2.4 sigma (18-35 keV) significance levels, where the former includes only the 2% systematic error of the non X-ray background, and the latter further takes into account possible near-by contaminating sources, respectively. Our confirmation of both soft and hard X-ray components during the late phase of the outburst strengthened the possibility that most magnetars are composed of the two spectral components, both in burst-active and less-active states. Together with a similar decay speed between the soft and hard components, their radiation mechanisms are suggested to be tightly related to each other. The 1-40 keV broadband spectrum was successfully fitted with the same model as used in the fit just after the onset of the outburst in 2009: a surface blackbody radiation with photoelectric absorption and a hard power-law. The blackbody flux decreased to be similar to 30% of that in 2009 while keeping its temperature at kT = 0.65 keV, suggesting a shrinking hotspot on the magnetar surface by a factor of 0.3. The hard power-law extended up to at least similar to 35 keV with a photon index of Gamma = 1.1 +/- 0.4, which was consistent with the 2009 value. The flux ratio, xi, of the 1-60 keV power-law to 1-60 keV thermal component was calculated to be xi = 1.2 +/- 0.7 at the late phase of the outburst for the first time. The obtained value follows the previously known negative correlation with the characteristic age, implying that the correlation holds for most of the magnetar states: no burst, onset and late phase of outbursts.

DOI： 10.1093/pasj/65.3.52

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Rapid spectral changes in the hard X-ray on a timescale down to similar to 0.1 s are studied by applying a "shot analysis" technique to the Suzaku observations of the black hole binary Cygnus X-1, performed on 2008 April 18 during the low/hard state. We successfully obtained the shot profiles, covering 10-200 keV with the Suzaku HXD-PIN and HXD-GSO detector. It is notable that the 100-200 keV shot profile is acquired for the first time owing to the HXD-GSO detector. The intensity changes in a time-symmetric way, though the hardness changes in a time-asymmetric way. When the shot-phase-resolved spectra are quantified with the Compton model, the Compton y-parameter and the electron temperature are found to decrease gradually through the rising phase of the shot, while the optical depth appears to increase. All the parameters return to their time-averaged values immediately within 0.1 s past the shot peak. We have not only confirmed this feature previously found in energies below similar to 60 keV, but also found that the spectral change is more prominent in energies above similar to 100 keV, implying the existence of some instant mechanism for direct entropy production. We discuss possible interpretations of the rapid spectral changes in the hard X-ray band.

DOI： 10.1088/2041-8205/767/2/L34

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We present observations of a transient He-like Fe Ka absorption line in Suzaku observations of the black hole binary Cygnus X-1 on 2011 October 5 near superior conjunction during the high/soft state, which enable us to map the full evolution from the start to the end of the episodic accretion phenomena or dips for the first time. We model the X-ray spectra during the event and trace their evolution. The absorption line is rather weak in the first half of the observation, but instantly deepens for similar to 10 ks, and weakens thereafter. The overall change in equivalent width is a factor of similar to 3, peaking at an orbital phase of similar to 0.08. This is evidence that the companion stellar wind feeding the black hole is clumpy. By analyzing the line with a Voigt profile, it is found to be consistent with a slightly redshifted Fe xxv transition, or possibly a mixture of several species less ionized than Fe xxv. The data may be explained by a clump located at a distance of similar to 10(10-12) cm with a density of similar to 10((-13)-(-11)) g cm(-3), which accretes onto and/or transits the line of sight to the black hole, causing an instant decrease in the observed degree of ionization and/or an increase in density of the accreting matter. Continued monitoring for individual events with future X-ray calorimeter missions such as ASTRO-H and AXSIO will allow us to map out the accretion environment in detail and how it changes between the various accretion states.

DOI： 10.1088/2041-8205/767/2/L35

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press  

To constrain the origin of the soft X-ray excess phenomenon seen in many active galactic nuclei, the intensity-correlated spectral analysis, developed by Noda et al. (2011, PASJ, 63, S925) for Markarian 509, was applied to wideband (0.5-45 keV) Suzaku data of five representative objects with a relatively weak reflection signature. They are the typical bare-nucleus type 1 Seyfert Fairall 9, the bright and typical type 1.5 Seyfert MCG-2-58-22, 3C 382, which is one of the X-ray brightest broad line radio galaxies, the typical Seyfert-like radio loud quasar 4C+74.26, and the X-ray brightest radio quiet quasar MR 2251-178. In all of them, soft X-ray intensities in energies below 3 keV were tightly correlated with that in 3-10 keV, but with significant positive offsets. These offsets, when calculated in finer energy bands, define a stable soft component in 0.5-3 keV. In each object, this component successfully explained the soft excess above a power-law fit. These components were interpreted in several alternative ways, including a thermal Comptonization component that is independent of the dominant power-law emission. This interpretation, considered physically most reasonable, is discussed from a viewpoint of Multi-Zone Comptonization, which was proposed for the black hole binary Cygnus X-1 (Makishima et al. 2008, PASJ, 60, 585). © 2013. Astronomical Society of Japan.

DOI： 10.1093/pasj/65.1.4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Abstract Light collection efficiency from BGO crystal scintillators of various sizes and shapes was measured by reading them using 1×1 cm 2 avalanche photo diodes. When the crystals have simple geometry, the light collection efficiency was found to depend on their size, shape and the read-out position through a rather well-defined empirical scaling relation. The light collection efficiency of tapered crystals was seen to depend on both the position of γ-ray irradiation, and the read-out position of the avalanche photo diodes. Using optical Monte-Carlo simulations, the relation was reproduced assuming plausible proper parameters for surface conditions and the attenuation length. This results were reproduced with a reasonable accuracy by optical Monte-Carlo simulations. Simple physical explanations are given to these geometrical effects. © 2013 Elsevier B.V.

DOI： 10.1016/j.nima.2013.03.022

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Aiming at a large array of transition edge sensors for future astrophysical missions such as DIOS, we have been developing a multilayer readout wiring. Superconducting signal and return lines made of Al sandwich a SiO2 insulation layer. With this approach, self and mutual inductances are minimized and self fielding of bias leads can be reduced. We fabricated a 20 × 20 transition-edge sensor (TES) array on the multilayer wiring. A series of TES fabrication processes including absorber deposition and membrane formation were tested. However, resistance measurements at room temperature suggest that process yield is not high ( ∼50 %). At low temperature, sharp superconducting transitions were observed for normal TES pixels, while their residual resistances were high (&gt
10mΩ) and the critical currents were low (&lt
10mu
A). Reasons for these phenomena and plans for a future TES array fabrication are discussed. © 2002-2011 IEEE.

DOI： 10.1109/TASC.2012.2231712

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Language：English   Publishing type：Research paper (international conference proceedings)  

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We present high-resolution X-ray spectra of cloud-shock interaction regions in the eastern and northern rims of the Galactic supernova remnant Puppis A, using the Reflection Grating Spectrometer on board the XMM-Newton satellite. A number of emission lines including K alpha triplets of He-like N, O, and Ne are clearly resolved for the first time. Intensity ratios of forbidden to resonance lines in the triplets are found to be higher than predictions by thermal emission models having plausible plasma parameters. The anomalous line ratios cannot be reproduced by effects of resonance scattering, recombination, or inner-shell ionization processes, but could be explained by charge-exchange emission that should arise at interfaces between the cold/warm clouds and the hot plasma. Our observations thus provide observational support for charge-exchange X-ray emission in supernova remnants.

DOI： 10.1088/0004-637X/756/1/49

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The neutron-star Low-Mass X-ray Binary Aquila X-1 was observed seven times in total with the Suzaku X-ray observatory from September 28 to October 30 in 2007, in the decaying phase of an outburst. In order to constrain the flux-dependent accretion geometry of this source over wider energy bands than employed in most previous studies, the present study utilized two out of seven data sets. The 0.8-31 keV spectrum on September 28, taken with the XIS and HXD-PIN for an exposure of 13.8 ks, shows an absorbed 0.8-31 keV flux of 3.6 x 10(-9) erg s(-1) cm(-2), together with typical characteristics of the soft state of this type of object. The spectrum was successfully explained by an optically thick disk emission plus a Comptonized blackbody component. Although these results are in general agreement with previous studies, the significance of a hard tail recently reported using the same data was inconclusive in our analysis. The spectrum acquired on October 9 for an exposure of 19.7 ks was detected over a 0.8-100 keV band with the XIS, HXD-PIN, and HXD-GSO, at an absorbed flux of 8.5 x 10(-10) erg s(-1) cm(-2) (in 0.8-100 keV). It shows characteristics of the hard state, and was successfully explained by the same two continuum components, but with rather different parameters, including much stronger thermal Comptonization, of which the seed photon source was identified with blackbody emission from the neutron-star surface. As a result, the accretion flow in the hard state is inferred to take the form of an optically-thick and geometrically-thin disk down to a radius of 21 +/- 4 km from the neutron star, and then turn into an optically thin nearly spherical hot flow.

DOI： 10.1093/pasj/64.4.72

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We report on the geometry of accretion disk and high-energy coronae in the strong Comptonization state (the very high/steep power law/hard intermediate state) based on a Suzaku observation of the famous Galactic black hole GX 339-4. These data were taken just before the peak of the 2006-2007 outburst, and the average X-ray luminosity in the 0.7-200 keV band is estimated to be 2.9 x 10(38) erg s(-1) for a distance of 8 kpc. We fit the spectrum with both simple (independent disk and corona) and sophisticated (energetically coupled disk and corona) models; all fits imply that the underlying optically thick disk is truncated significantly before the innermost stable circular orbit around the black hole. We show this directly by a comparison with similar broadband data from a disk-dominated spectrum at almost the same luminosity observed by XMM-Newton and RXTE 3 days after the Suzaku observation. During the Suzaku observation, the quasi-periodic oscillation (QPO) frequency changes from 4.3 Hz to 5.5 Hz, while the spectrum softens. The energetically coupled model gives a corresponding 5%+/- 8% decrease in the derived inner radius of the disk. While this is not significant, it is consistent with the predicted change in QPO frequency from the Lense-Thirring precession of the hot flow interior to the disk and/or a deformation mode of this flow, as a higher QPO frequency implies a smaller size scale for the corona. This is consistent with the truncated disk extending further inward toward the black hole.

DOI： 10.1088/0004-637X/753/1/65

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We report on a discovery of a diffuse nebula containing a pointlike source in the southern blowout region of the Cygnus Loop supernova remnant, based on Suzaku and XMM-Newton observations. The X-ray spectra from the nebula and the pointlike source are well represented by an absorbed power-law model with photon indices of 2.2 +/- 0.1 and 1.6 +/- 0.2, respectively. The photon indices as well as the flux ratio of F-nebula/F-pointlike similar to 4 lead us to propose that the system is a pulsar wind nebula, although pulsations have not yet been detected. If we attribute its origin to the Cygnus Loop supernova, then the 0.5-8 keV luminosity of the nebula is computed to be 2.1 x 10(31) (d/540 pc)(2) erg s(-1), where d is the distance to the Loop. This implies a spin-down loss-energy E. similar to 2.6 x 10(35) (d/540 pc)(2) erg s(-1). The location of the neutron star candidate, similar to 2 degrees away from the geometric center of the Loop, implies a high transverse velocity of similar to 1850 (theta/2 degrees) (d/540 pc) (t/10 kyr)(-1) km s(-1), assuming the currently accepted age of the Cygnus Loop.

DOI： 10.1088/2041-8205/754/1/L7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results of a systematic study of pileup phenomena seen in the X-ray Imaging Spectrometer, an X-ray CCD instrument, onboard the Suzaku observatory. Using a data set of observed sources in a wide range of brightness and spectral hardness, we characterized the pileup fraction, spectral hardening, and grade migration as a function of the observed count rate in a frame per pixel. Using the pileup fraction as a measure of the degree of pileup, we found that the relative spectral hardening (the hardness ratio normalized to the intrinsic spectral hardness), branching ratio of split events, and that of detached events increase monotonically as the pileup fraction increases, despite the variety of brightness and hardness of the sample sources. We derived the pileup fraction as a function of radius used for event extraction. Upon practical considerations, we found that events outside of the radius with a pileup fraction of 1% or 3% are useful for spectral analysis. We present relevant figures, tables, and software for the convenience of users who wish to apply our method for their data reduction of piled-up sources.

DOI： 10.1093/pasj/64.3.53

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary system, observed with the hard X-ray detector of the Japanese X-ray satellite Suzaku in 2006 March for a net exposure of similar to 88 ks. The source was detected at an average 10-60 keV flux of similar to 4 x 10(-10) erg cm(-2) s(-1). The phase-averaged spectrum is reproduced well by combining a negative and positive power-law times exponential cutoff (NPEX) model modified at similar to 37 keV by a cyclotron resonance scattering feature (CRSF). The phase-resolved analysis shows that the spectra at the bright phases are well fit by the NPEX with CRSF model. On the other hand, the spectrum in the dim phase lacks the NPEX high-energy cutoff component, and the CRSF can be reproduced by either an emission or an absorption profile. When fitting the dim phase spectrum with the NPEX plus Gaussian model, we find that the feature is better described in terms of an emission rather than an absorption profile. The statistical significance of this result, evaluated by means of an F test, is between 2.91 x 10(-3) and 1.53 x 10(-5), taking into account the systematic errors in the background evaluation of HXD-PIN. We find that the emission profile is more feasible than the absorption one for comparing the physical parameters in other phases. Therefore, we have possibly detected an emission line at the cyclotron resonance energy in the dim phase.

DOI： 10.1088/0004-637X/751/1/35

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Publishing type：Research paper (scientific journal)  

We report on an X-ray spectral analysis of the black hole candidate XTE J1752-223 in the 2009-2010 outburst, utilizing data obtained with the MAXI/Gas Slit Camera (GSC), the Swift/XRT, and Suzaku, which work comple-mentarily. As already reported by Nakahira et al. (2010, PASJ, 62, L27), MAXI monitored the source continuously throughout the entire outburst for about eight months. All of the MAXI/GSC energy spectra in the high/soft state, lasting for 2 months, are well represented by a multi-color disk plus power-law model. The innermost disk temperature changed from ∼0.7 keV to ∼0.4 keV and the disk flux decreased by an order of magnitude. Nevertheless, the innermost radius is constant at ∼41 D 3.5 (cos i) -1/2 km, where D 3.5 is the source distance in units of 3.5kpc and i the inclination. The multi-color disk parameters obtained with the MAXI/GSC are consistent with those with the Swift/XRT and Suzaku. The Suzaku data also suggest a possibility that the disk emission is slightly Comptonized, which could account for broad iron-K features reported previously. Assuming that the obtained innermost radius represents the innermost stable circular orbit for a non-rotating black hole, we estimate the mass of the black hole to be 5.51 ± 0.28 M ⊙ D 3.5 (cos -1/2 , where the correction for the stress-free inner boundary condition and color hardening factor of 1.7 are taken into account. If the inclination is less than 49°, as suggested from radio monitoring of transient jets, and the soft-to-hard transition in 2010 April occurred at 1%-4% of Eddignton luminosity, the fitting of the Suzaku spectra with a relativistic accretion-disk model derives constraints on the mass and the distance to be 3.1-55M ⊙ and 2.3-22 kpc, respectively. This confirms that the compact object in XTE J1752-223 is a black hole. © 2012. Astronomical Society of Japan.

DOI： 10.1093/pasj/64.1.13

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Language：English   Publishing type：Research paper (international conference proceedings)  

The joint JAXA/NASA ASTRO-H mission is the sixth in a series of highly successful X-ray missions initiated by the Institute of Space and Astronautical Science (ISAS). ASTRO-H will investigate the physics of the highenergy universe via a suite of four instruments, covering a very wide energy range, from 0.3 keV to 600 keV. These instruments include a high-resolution, high-Throughput spectrometer sensitive over 0.3-12 keV with high spectral resolution of ?E 5 7 eV, enabled by a micro-calorimeter array located in the focal plane of thin-foil X-ray optics
hard X-ray imaging spectrometers covering 5-80 keV, located in the focal plane of multilayer-coated, focusing hard X-ray mirrors
a wide-field imaging spectrometer sensitive over 0.4-12 keV, with an X-ray CCD camera in the focal plane of a soft X-ray telescope
and a non-focusing Compton-camera type soft gamma-ray detector, sensitive in the 40-600 keV band. The simultaneous broad bandpass, coupled with high spectral resolution, will enable the pursuit of a wide variety of important science themes. © 2012 SPIE.

DOI： 10.1117/12.926190

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Language：English   Publishing type：Research paper (international conference proceedings)  

We analyzed Suzaku data of Cygnus X-1 in the low/hard state, acquired on 25 occasions from 2005 to 2009, over 0.5-300 keV with a total exposure of ∼450 ks. Among the observations, its luminosity changed by a factor of ∼3. We found two different types of spectral changes in rather model independent manners. One is an increase of variability in E &lt
10 keV on time scales of days to months, revealed via a direct comparison among the 25 spectra. The other is a decrease of variability in E &lt
2 keV on time scales of 1-2 seconds, derived by using intensity-correlated spectral changes for each observation. The two spectral changes can be understood by considering that the accretion flow consists of a cool disk with a temperature of ∼0.2 keV surrounded by inhomogeneous coronae. © 2012 American Institute of Physics.

DOI： 10.1063/1.3696148

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Language：English   Publishing type：Research paper (international conference proceedings)  

The current status and the improvements of in-orbit calibration in the Hard X-ray Detector (HXD) on board Suzaku are presented. We have been extensively monitoring and calibrating the in-orbit HXD performance, and succeeded in keeping all the sensors working property without any significant troubles since the launch. To reduce the increasing thermal noise events due to radiation damage in the HXD-PIN, we have raised the analog/digital threshold levels and updated the corresponding responses of the PIN. Performing the calibration of the energy scale of the GSO, we have improved the accuracy of the energy scale and modeling of gain variations, and released the reprocessed data/background and the responses since April of 2010. These revised data of the GSO is usable down to 50 keV, consequently allowing us to utilize overlapping energy ranges of 50-70 keV between the PIN and the GSO. Based on these improvements, we have reproduced the HXD spectra of the Crab Nebula over 10-500 keV with the broken power law with a cutoff at about 120 keV. © 2012 American Institute of Physics.

DOI： 10.1063/1.3696159

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

To understand flare mechanisms of SFXTs, we analyzed Suzaku public data of AXJ161929-4945. The data covered a large flare with a rise time of about 500 sec and a duration of about 3 hours. Over a 1-40 keV band, the spectra were very similar between the flare and quiescence periods. The column density was not different between the two spectra by more than 10%. A narrow Fe-line were very clearly detected in the quiescence, but disappeared in the flare. These results suggest that the flare occured due to strong magnetic fields of the neutron star.

DOI： 10.1063/1.3696219

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The scientific objective of the X-ray Advanced Concepts Testbed (XACT) is to measure the X-ray polarization properties of the Crab Nebula, the Crab pulsar, and the accreting binary Her X-1. Polarimetry is a powerful tool for astrophysical investigation that has yet to be exploited in the X-ray band, where it promises unique insights into neutron stars, black holes, and other extreme-physics environments. With powerful new enabling technologies, XACT will demonstrate X-ray polarimetry as a practical and flight-ready astronomical technique. Additional technologies that XACT will bring to flight readiness will also provide new X-ray optics and calibration capabilities for NASA missions that pursue space-based X-ray spectroscopy, timing, and photometry.

DOI： 10.1117/12.926418

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

We conducted 25 Suzaku observations of Cyg X-1 in the Low/Hard State, with a total exposure of about 450 ks, Here, we analyzed the data from the Hard X-ray Detector (HXD). From results obtained from spectral and timing analysis, we derived some picture of evolution of the accretion flow in the Low/Hard State. and the cool disk to intrude more deeply therein (Torii et al. 2011). On 2010 December 16, a Suzaku ToO observation of Cyg X-1 was performed to benefit from the most recent High/Soft State found with MAXI. A brief analysis of the data is presented in this paper.

DOI： 10.1063/1.3696163

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Aiming at understanding the soft and hard states of accreting weak-field neutron stars, archival Suzaku data of the recurrent transient Aql X-1, taken during a 2007 outburst, were analyzed. In one data set, where the object was in the soft state, the 1-30 keV spectrum was reproduced by a disk blackbody plus a Comptonized blackbody components, which is consistent with previous studies. Other three data sets were taken during the typical hard state, with a factor similar to 6 lower luminosity than the first one. The source was detected up to similar to 100 keV on these occasions, and the wide-band spectra were reproduced by the same model composition as the soft state, but with much stronger Comptonization and a larger disk radii. The three hard-state spectra exhibited comparable luminosities, and gave similar model parameters. Therefore, the spectrum of this source is considered to be determined rather uniquely by the mass accretion rate.

DOI： 10.1063/1.3696217

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

ASTRO-H is the next generation JAXA X-ray satellite, intended to carry instruments with broad energy coverage and exquisite energy resolution. The Soft Gamma-ray Detector (SGD) is one of ASTRO-H instruments and will feature wide energy band (60-600 keV) at a background level 10 times better than the current instruments on orbit. The SGD is complimentary to ASTRO-H's Hard X-ray Imager covering the energy range of 5-80 keV. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield where Compton kinematics is utilized to reject backgrounds. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) sensors. Good energy resolution is afforded by semiconductor sensors, and it results in good background rejection capability due to better constraints on Compton kinematics. Utilization of Compton kinematics also makes the SGD sensitive to the gamma-ray polarization, opening up a new window to study properties of gamma-ray emission processes. In this paper, we will present the detailed design of the SGD and the results of the final prototype developments and evaluations. Moreover, we will also present expected performance based on the measurements with prototypes.

DOI： 10.1117/12.925977

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AIP Conference Proceedings  

The Crab Nebula had been believed to be a stable standard candle for historical X-ray instruments for many years. Recently it was found that a hard X-ray flux (15-100 keV) of Crab Nebula fluctuated by 10 over 10 years. The origin of the long-term variation is still unclear, but the nature of the Crab Nebula is now hot topic both on science and hardware developments. The HXD onboard Suzaku has the highest sensitivity in the 10-600 keV band. Hence it is useful to search for flux variations and possible spectral changes. We performed systematic studies on Crab X-ray spectra in the 10-600 keV band with the HXD, by using 12 observations of Crab until 2010. In this paper, we summarized a hard X-ray study of Crab with the HXD. © 2012 American Institute of Physics.

DOI： 10.1063/1.3696196

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Improvements of the in-orbit calibration of GSO scintillators in the Hard X-ray Detector aboard Suzaku are reported. To resolve an apparent change in the energy scale of GSO, which appeared across the launch for unknown reasons, consistent and thorough re-analyses of both pre-launch and in-orbit data have been performed. With laboratory experiments using spare hardware, the pulse-height offset, corresponding to zero energy input, was found to change by similar to 0.5% of the full analog voltage scale, depending on the power supply. Furthermore, by carefully calculating all of the light outputs of secondaries from activation lines used in the in-orbit gain determination, their energy deposits in GSO were found to be effectively lower, by several percent, than their nominal energies. Taking both of these effects into account, the in-orbit data agree with the on-ground measurements within similar to 5%, without employing the artificial correction introduced in previous work (Kokubun et al. 2007, PASJ, 59, S53). With this knowledge, we updated the data processing, the response, and the auxiliary files of GSO, and reproduced the HXD-PIN and HXD-GSO spectra of the Crab Nebula over 12-300 keV by a broken power-law with a break energy of similar to 110 keV.

DOI： 10.1093/pasj/63.sp3.S645

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

From 2005 to 2009, 25 observations of Cyg X-1 were performed with Suzaku, achieving a total exposure of 446 ks. In all observations, the source was found in the low/hard state, while the 1.5-12.0 keV count rate of the All-Sky Monitor onboard RXTE varied by a factor of similar to 3. In each observation, the 10-60 keV HXD-PIN spectrum and the 60-400 keV HXD-GSO spectrum were fitted successfully by a thermal Comptonization model plus reflection by a thick neutral material. As the soft X-ray intensity increased, the Compton y-parameter was found to decrease from 1.0 to 0.6, while the solid angle of reflection increased by similar to 30%. Also conducted was a timing analysis over a frequency range of 10(-3)-10 Hz. As the source became brighter in soft X-rays, the characteristic frequency of the hard X-ray variation increased from 0.03 to 0.3 Hz, while the fractional hard X-ray variation integrated over 10(-3)-10(-2) Hz decreased by a factor of similar to 5. The signals in the 60-200 keV band were generally found to vary on shorter time scales than those in the 10-60 keV band. These spectral and timing results can be consistently interpreted by presuming that increases in the mass accretion rate cause the Comptonizing hot corona to shrink, while the optically-thick disk to intrude deeper therein.

DOI： 10.1093/pasj/63.sp3.S771

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The Type I Seyfert galaxy Markarian 509 was observed with Suzaku in 2010 November, for a gross time span of 2.2 days. The timing and spectral properties of the 0.5-45 keV X-rays, detected with the XIS and HXD, consistently revealed the presence of a soft spectral component that remained constant while the total X-ray intensity varied by +/- 10%. This stable soft component, found in the 0.5-3.0 keV range, was interpreted as being a result of thermal Comptonization in a corona with a temperature of similar to 0.5 keV and an optical depth of similar to 18. The time-avearged 0.5-45 keV Suzaku spectrum was reproduced successfully, as a combination of this thermal Comptonization component, a harder power-law of photon index similar to 1.8, moderate reflection, and an iron K-emission line. By analyzing four archival Suzaku datasets of the same object obtained in 2006, the thermal Comptonization component, which was stable during 2.2-day pointing in 2010, was found to vary on time scales of a few weeks, independently of the power-law component. Implications of these results are discussed in terms of a "multi-zone Comptonization" view, obtained with Suzaku from the black-hole binary Cygnus X-1.

DOI： 10.1093/pasj/63.sp3.S925

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Focusing on hard X-ray variability, we reanalyzed Suzaku data of the Type I Seyfert galaxy MCG-6-30-15 obtained in 2006. Intensity-sorted spectroscopy and a principal-component analysis consistently revealed a very hard component that varies independently of the dominant power-law emission. Although the exact nature of this hard component has not yet been identified, it can be modeled as a power-law with a photon index of 2 affected by a partial covering absorption, or as a thermal Comptonization emission with a relatively large optical depth. When this component is included in the fitting model, the time-averaged 2.5-55 keV spectrum of MCG-6-30-15 can be reproduced successfully by invoking a mildly broadened iron line with its emission region located at greater than or similar to 8 times the gravitational radii from the central black hole, and a moderate reflection with a covering fraction of similar to 3.4 pi. This result implies that the solution of a highly spinning black hole in MCG-6-30-15, obtained by Miniutti et al. (2007, PASJ, 59, S315) using the same Suzaku data as ours, is a model-dependent result.

DOI： 10.1093/pasj/63.2.449

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Blackwell Publishing Ltd  

The Gamma-Ray Observation of Winter Thunderclouds (GROWTH) experiment, consisting of two radiation detection subsystems, has been operating since 2006 on the premises of Kashiwazaki-Kariwa nuclear power plant located at the coastal area of Japan Sea. By February 2010, GROWTH detected seven long-duration γray emissions associated with winter thunderstorms. Of them, two events, obtained on 13 December 2007 and 25 December 2008, are reported. On both occasions, all inorganic scintillators (NaI, CsI, and BGO) of the two subsystems detected significant γ ray signals lasting for &gt
1 min. Neither of these two events were associated with any lightning. In both cases, the γray energy spectra extend to 10 MeV, suggesting that the detected γrays are produced by relativistic electrons via bremsstrahlung. Assuming that the initial photon spectrum at the source is expressed by a power law function, the observed photons can be interpreted as being radiated from a source located at a distance of 290-560 m for the 2007 event and 110-690 m for the 2008 one, both at the 90% confidence level. Employing these photon spectra, the number of relativistic electrons is estimated as 10&lt
sup&gt
9&lt
/sup&gt
-10 &lt
sup&gt
11&lt
/sup&gt
. The estimation generally agrees with those calculated on the basis of the relativistic runaway electron avalanche model. A GROWTH photon spectrum, summed over three individual events including the present two events and another reported previously, has similar features including a cutoff energy, to an averaged spectrum of terrestrial γ ray flashes. Copyright 2011 by the American Geophysical Union.

DOI： 10.1029/2010JD015161

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：EDP SCIENCES S A  

Context. White dwarfs (WDs) in cataclysmic variables (CVs) are important experimental laboratories where the electron degeneracy is taking place on a macroscopic scale. Magnetic CVs increase in number especially in the hard X-ray band (greater than or similar to 10 keV) thanks to sensitive hard X-ray missions.
Aims. From X-ray spectroscopy, we estimate the masses of nearby WDs in moderately-magnetized CVs, or Intermediate Polars (IPs).
Methods. Using the Suzaku satellite, we aquired wide-band spectra of 17 IPs, covering 3-50 keV. An accretion column model of Suleimanov et al. (2005, A&A, 435, 191) and an optically-thin thermal emission code were used to construct a spectral emission model of IPs with resolved Fe emission lines. By simultaneously fitting the Fe line complex and the hard X-ray continuum of individual spectra, the shock temperature and the WD mass were determined with a better accuracy than in previous studies.
Results. We determined the WD masses of the 17 IPs with statistical fitting errors of less than or similar to 0.1-0.2 M-circle dot in many cases. The WD mass of a recently-found IP, IGR J17195-4100, was also estimated for the first time (1.03(-0.22)(+0.24) M-circle dot). The average WD mass of the sample is 0.88 +/- 0.25 M-circle dot. When our results were compared with previous X-ray mass determinations, we found significant deviation in a few systems although the reason of this is unclear. The iron abundance of the accreting gas was also estimated, and confirmed the previously reported sub-solar tendency in all sources with better accuracy.

DOI： 10.1051/0004-6361/201014542

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The black hole binary system LMC X-3 has been observed by virtually every X-ray mission since the inception of X-ray astronomy. Among the persistent sources, LMC X-3 is uniquely both habitually soft and highly variable. Using a fully relativistic accretion disk model, we analyze hundreds of spectra collected during eight X-ray missions that span 26 years. For a selected sample of 391 RXTE spectra, we find that to within approximate to 2% the inner radius of the accretion disk is constant over time and unaffected by source variability. Even considering an ensemble of eight X-ray missions, we find consistent values of the radius to within approximate to 4%-6%. Our results provide strong evidence for the existence of a fixed inner-disk radius. The only reasonable inference is that this radius is closely associated with the general relativistic innermost stable circular orbit. Our findings establish a firm foundation for the measurement of black hole spin.

DOI： 10.1088/2041-8205/718/2/L117

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We observed the soft gamma repeater SGR 0501+4516 with Suzaku for similar to 51 ks on 2008 August 26-27, about 4 days after its discovery. Following the first paper, which reported on the persistent soft X-ray emission and the wide-band spectrum of an intense short burst, this paper presents an analysis of the persistent broadband (1-70 keV) spectra of this source in outburst, taken with the X-ray Imaging Spectrometer (XIS) and the Hard X-ray Detector (HXD). Pulse-phase folding in the 12-35 keV HXD-PIN data on an ephemeris based on multi-satellite timing measurements at soft X-rays revealed the pulsed signals at greater than or similar to 99% confidence in the hard X-ray band. The wide-band spectrum clearly consists of a soft component and a separate hard component, crossing over at similar to 7 keV. When the soft component is modeled by a blackbody plus a Comptonized blackbody, the hard component exhibits a 20-100 keV flux of 4.8(-0.6)(+0.8) (stat.)(-0.4)(+ 0.8) (sys.) x 10(-11) erg s(-1) cm(-2) and a photon index of Gamma = 0.79(-0.18)(+ 0.01) (sys.). The hard X-ray data are compared with those obtained by INTEGRAL about 1 day later. Combining the present results with those on other magnetars, we discuss a possible correlation between the spectral hardness of magnetars and their characteristic age and magnetic field strengths.

DOI： 10.1088/0004-637X/715/1/665

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report on results of the 2006 April multiwavelength campaign of SS 433, focusing on X-ray data observed with Suzaku at two orbital phases (in- and out-of-eclipse phases) and on simultaneous optical spectroscopic observations. Analyzing the Fe XXV K alpha lines originating from the jets, we detected a rapid variability of the Doppler shifts, dz/dt approximate to 0.019/0.33 d(-1), which is larger than those expected from the precession and/or nodding motion. This phenomenon probably corresponds to "jitter" motions observed for the first time in X-rays, for which significant variabilities in both the jet angle and the intrinsic speed are required. From time lags between optical Doppler curves and X-ray ones, we estimated a distance between the optical jets and the base to be similar to (3-4) x 10(14)cm. Based on the radiatively cooling jet model, we determined that the innermost temperatures of the jets are T-0 = 13 +/- 2 keV for the out-of-eclipse phase and 16 3 keV for the in-eclipse (the average of the blue and red jets) from the line intensity ratio of Fe xxv Ka and Fe XXVI K alpha. While the broad-band-continuum spectra over the 5-40 keV band in eclipse is consistent with a multitemperature-bremsstrahlung emission expected from the jets and its reflection component from cold matter, the out-of-eclipse spectrum is harder than the jet emission with the base temperature determined above, implying the presence of an additional hard component.

DOI： 10.1093/pasj/62.2.323

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

Suzaku has enabled us to study wide-band spectral and timing properties of black-hole binaries and AGNs more accurately than ever, and revealed how the continuum definition can affect Fe-K line profiles. We have reproduced 0.5-300 keV spectra of Cyg X-1 and GRO J1655-40 in terms of thermal Comptonization in highly inhomogeneous coronae. In both objects, R-in was constrained by the Fe-K line profile and soft excess as similar to 10 R-g, as opposed to the relativistic Fe-K line reported in the literature. We also re-analyzed the 0.7-300 keV Suzaku spectra of OX 339-4, and found that a careful modeling of the continuum leads to R-in &gt; R-g(Yamada et al. 2009), again in disagreement with Miller et al. (2008). Furthermore, through a systematic analysis of AGNs, we discovered a hard spectral component in the HXD-PIN band, which varies independently of the powerlaw. Taking this into account, the time-averaged spectra of MCG-6-30-15 have been explained by invoking neither a large refection fraction, nor an extreme broad Fe-K line. The essence here is that the hard X-ray (20-40 keV) bump may be partially explained as an additional Comptonization component. Our results indicate that the extremely relativistic Fe-K line reported for some objects is not a unique solution, and depends in many cases on the continuum modeling.

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Language：English   Publishing type：Research paper (international conference proceedings)  

Hard X-ray Detector (HXD) onboard Suzaku, the Japanese 5th X-ray observatory, consists of 64 PIN photo diodes with 2 mm thickness (10-70 keV) and 16 phoswich detectors using 5 mm-thick GSO scintillators and BGO active collimators (40-600 keV), and these are surrounded by 20 units of BGO Active shields. All the detector units have been working well with no significant troubles in four and a half years since the launch on July 2005, and given many important scientific results. In this paper, we report the recent status of onorbit calibrations for PIN/GSO detectors. For the PIN, analog/digital threshold levels of both in-orbit and on-ground are raised up to avoid the increasing noise events due to in-orbit radiation damage. For the GSO, the accuracy of the energy scale and modeling of gain variations are improved, and newly calibrated data set including background files and response matrices are released on April 2010. © 2010 SPIE.

DOI： 10.1117/12.856888

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Other Link： http://orcid.org/0000-0003-3529-3029

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The wide-band Suzaku spectra of the black hole (BH) binary GX 339-4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within similar to 3' of the image center) and telemetry saturation of the X-ray Imaging Spectrometer (XIS) data were carefully considered. The source was detected up to similar to 300 keV, with an unabsorbed 0.5-200 keV luminosity of 3.8 x 10(38) erg s(-1) at 8 kpc. The spectrum can be approximated by a power law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2' of the image center, the Fe K line appeared extremely broad, suggesting a high BH spin as already reported by Miller et al. based on the same Suzaku data and other CCD data. When the XIS data accumulation is further limited to &gt; 3' to avoid event pileup, the Fe K profile becomes narrower, and a marginally better solution appears which suggests that the inner disk radius is 5-14 times the gravitational radius (1 sigma), though a maximally spinning BH is still allowed by the data at the 90% confidence level. Consistently, the optically thick accretion disk is inferred to be truncated at a radius 5-32 times the gravitational radius. Thus, the Suzaku data allow an alternative explanation without invoking a rapidly spinning BH. This inference is further supported by the disk radius measured previously in the High/Soft state.

DOI： 10.1088/0004-637X/707/2/L109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a total good exposure time of 100 ks. We present an analysis of the Suzaku XIS data, in which we confirm that the 0.5-2 keV spectra of the interstellar medium (ISM) are well-represented by a two-temperature model. The cool and hot ISM temperatures are 0.23 +/- 0.01 and 0.58 +/- 0.01 keV, respectively. Suzaku's excellent spectral sensitivity has enabled us to measure the metal abundances of O, Ne, Mg, Si, and Fe of the ISM for the first time. The resultant abundance pattern of 0, Mg, Si, and Fe is consistent with that of the new solar abundance table of Lodders (2003, ApJ, 591, 1220), rather than Anders and Grevesse (1989, Geochim. Cosmochim. Acta, 53, 197). This suggests that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.

DOI： 10.1093/pasj/61.5.941

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

In 2006 June, the obscured low-luminosity active galactic nucleus in the nearby Seyfert 1.9 galaxy NGC 4258 was observed with Suzaku for similar to 100 ks. Utilizing the XIS and the HXD, the nucleus emission was detected over a similar to 2 to similar to 40 keV range, with ail unabsorbed 2-10 keV luminosity of similar to 8 x 10(40)) erg s(-1); it varied by a factor of similar to 2 during the observation. Its 2-40 keV spectrum is reproduced by a single power law with a photon index of Gamma similar to 2.0, absorbed by an equivalent hydrogen column of similar to 1.0 x 10(23) cm(2). The spectrum within 4' of the nucleus also required a softer thin-thermal emission, as well as an intermediate hardness component, attributable to integrated point sources. A weak neutral Fe-K alpha florescence line was detected at ail equivalent width of similar to 40eV. A cold reflection component was not required by the data, with the reflector solid angle Omega seen from the nucleus constrained as Omega/2 pi less than or similar to 0.3, assuming a general case of 60 degrees inclination. The results suggest that the cold reflecting material around the nucleus is localized along Our line of sight, rather than forming a thick torus.

DOI： 10.1093/pasj/61.2.309

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present the first Suzaku observation of the new Soft Gamma Repeater, SGR 0501+4516, performed on 2008 August 26, four days after the onset of bursting activity of this new member of the magnetar family. The soft X-ray persistent emission was detected with the X-ray Imaging Spectrometer (XIS) at a 0.5-10 keV flux of 3.8 x 10-(11) erg s(-1) cm(-2), with a spectrum well fitted by an absorbed blackbody plus power-law model. The source pulsation was confirmed at a period of 5.762072 +/- 0.000002 s, and 32 X-ray bursts were detected by the XIS, four of which were also detected at higher energies by the Hard X-ray Detector (HXD). The strongest burst, which occurred at 03:16:16.9 (UTC), was so bright that it caused instrumental saturation, but its precursor phase, lasting for about 200 ms, was detected successfully over the 0.5-200 keV range, with a fluence of similar to 2.1 x 10(-7) erg cm-2 and a peak intensity of about 89 crab. The entire burst fluence is estimated to be similar to 50 times higher. The precursor spectrum was very hard, and well modeled by a combination of two blackbodies. We discuss the bursting activity and X/gamma-ray properties of this newly discovered Soft Gamma Repeater in comparison with other members of the class.

DOI： 10.1088/0004-637X/693/2/L122

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

The Soft Gamma-ray Detector (SGD) on board ASTRO-H (Japanese next high-energy astrophysics mission) is a Compton telescope with narrow field-of-view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (50-600 keV) at a background level 10 times better than that of the Suzaku Hard X-ray Detector, and is complimentary to the Hard X-ray Imager on board ASTRO-H with an energy coverage of 5-80 keV. Excellent energy resolution is the key feature of the SGD, allowing it to achieve good background rejection capability taking advantage of good angular resolution. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of gamma-ray emission processes. Here we describe the instrument design of the SGD, its expected performance, and its development status.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Physics Publishing  

The wide-band Suzaku spectra of the black hole (BH) binary GX 339-4, acquired in 2007 February during the Very High state, were reanalyzed. Effects of event pileup (significant within ∼3′ of the image center) and telemetry saturation of the X-ray Imaging Spectrometer (XIS) data were carefully considered. The source was detected up to ∼300keV, with an unabsorbed 0.5-200keV luminosity of 3.8 × 1038ergs-1 at 8kpc. The spectrum can be approximated by a power law of photon index 2.7, with a mild soft excess and a hard X-ray hump. When using the XIS data outside 2′ of the image center, the Fe K line appeared extremely broad, suggesting a high BH spin as already reported by Miller etal. based on the same Suzaku data and other CCD data. When the XIS data accumulation is further limited to &gt
3′ to avoid event pileup, the Fe K profile becomes narrower, and a marginally better solution appears which suggests that the inner disk radius is 5-14 times the gravitational radius (1σ), though a maximally spinning BH is still allowed by the data at the 90% confidence level. Consistently, the optically thick accretion disk is inferred to be truncated at a radius 5-32 times the gravitational radius. Thus, the Suzaku data allow an alternative explanation without invoking a rapidly spinning BH. This inference is further supported by the disk radius measured previously in the High/Soft state. © 2009 The American Astronomical Society.

DOI： 10.1088/0004-637X/707/2/L109

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Language：English   Publishing type：Research paper (international conference proceedings)  

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The Soft Gamma-ray Detector (SGD) on board ASTRO-H (Japanese next high-energy astrophysics mission) is a Compton telescope with narrow field-of-view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor detector system which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (50-600 keV) at a background level 10 times better than that of the Suzaku Hard X-ray Detector, and is complimentary to the Hard X-ray Imager on board ASTRO-H with an energy coverage of 5-80 keV. Excellent energy resolution is the key feature of the SGD, allowing it to achieve good background rejection capability taking advantage of good angular resolution. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of gamma-ray emission processes. Here we describe the instrument design of the SGD, its expected performance, and its development status. ©2009 IEEE.

DOI： 10.1109/NSSMIC.2009.5402092

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigate the emergence of strange baryons in the dynamical collapse of a nonrotating massive star to a black hole using neutrino-radiation hydrodynamical simulations in general relativity. By following the dynamical formation and collapse of a nascent proto-neutron star from the gravitational collapse of a 40 M(circle dot) star adopting a new hyperonic equation-of-state (EOS) table, we show that the hyperons do not appear at the core bounce but populate quickly similar to 0.5-0.7 s after the bounce to trigger the recollapse to a black hole. They start to show up off center owing to high temperatures and later prevail at center when the central density becomes high enough. The neutrino emission from the accreting proto-neutron star with the hyperonic EOS stops much earlier than the corresponding case with a nucleonic EOS, while the average energies and luminosities are quite similar in the two cases. These features of the neutrino signal are a potential probe of the emergence of new degrees of freedom inside the black hole forming collapse.

DOI： 10.1088/0004-637X/690/1/L43

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10-600 keV, by utilizing PIN photodiodes and GSO scintillators; mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information, The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1 sigma systematic error is estimated to be less than 3% (PIN 15-40 keV) and 1% (GSO 50-100 keV) for more than 10 ks exposure.

DOI： 10.1093/pasj/61.sp1.S17

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The broad-band 1-300 keV Suzaku spectrum of IGR J17497-2821, the X-ray transient discovered by INTEGRAL in 2006 September, is presented. Suzaku observed IGR J17497-2821 on September 25, eight days after its discovery, for a net exposure of about 53 ks. During the Suzaku observation, IGR J17497-2821 is very bright, 2 x 10(37) erg s(-1) at 8 kpc in the 1-300 keV range, and shows a hard spectrum, typical of black hole candidates in the low-hard state. Despite the multi-mission X-ray monitoring of the source, only with Suzaku is it possible to obtain a broad-band spectrum in the 1-300 keV range with a very high signal to noise ratio. A sum of a multi-color disc and a thermal Comptonization component with mild reflection is a good representation of our IGR J17497-2821 Suzaku spectrum. The spectral properties of the accretion disc as well as the cut-off energy in the spectrum at about 150 keV are clearly detected and constrained. We discuss the implications on the physical model used to interpret the data and the comparison with previous results.

DOI： 10.1093/pasj/61.sp1.S107

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

A report is presented on Suzaku observations of the ultra-luminous X-ray source X-1 in the starburst galaxy M 82, made three times in 2005 October for an exposure of similar to 30 ks each. The XIS signals from a region of radius 3' around the nucleus defined a 2-10 keV flux of 2.1 x 10(-11) erg s(-1) cm(-2) attributable to point sources. The 3.2-10 keV spectrum was slightly more convex than a power-law with a photon index of 1.7. In all observations, the HXD also detected signals from M 82 up to similar to 20 keV, at a 12-20 keV flux of 4.4 x 10(-12) erg s(-1) cm(-2). The HXD spectrum was steeper than that of the XIS. The XIS and HXD spectra can be jointly reproduced by a cutoff power-law model, or similar curved models. Of the detected wide-band signals, 1/3 to 2/3 are attributable to X-1, while the remainder to other discrete sources in M 82. Regardless of the modeling of these contaminants, the spectrum attributable to X-I is more curved than a power-law, with a bolometric luminosity of (1.5-3) x 10(40) ergs(-1). These results are interpreted as Comptonized emission from a black hole of 100-200 solar masses, radiating roughly at the Eddington luminosity.

DOI： 10.1093/pasj/61.sp1.S263

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The black-hole binary Cygnus X-1 was observed for 17 ks with the Suzaku X-ray observatory in 2005 October, while it was in a low/hard state with a 0.7-300 keV luminosity of 4.6 x 10(37) ergs(-1). The XIS and HXD spectra, spanning 0.7-400 keV, were reproduced successfully, incorporating a cool accretion disk and a hot Comptonizing corona. The corona is characterized by an electron temperature of similar to 100 keV, and two optical depths of similar to 0.4 and similar to 1.5, which account for the softer and harder continua, respectively. The disk has an innermost temperature of similar to 0.2keV, and is thought to protrude half way into the corona. The disk not only provides seed photons to the Compton cloud, but also produces a soft spectral excess, a mild reflection hump, and a weakly broadened iron line. A comparison with the Suzaku data on GRO J1655-40 reveals several interesting spectral differences, which can mostly be attributed to inclination effects, assuming that the disk has a flat geometry while the corona is grossly spherical. An intensity-sorted spectroscopy indicates that the continuum becomes less Comptonized when the source flares up on time scales of 1-200 s, while the underlying disk remains unchanged.

DOI： 10.1093/pasj/60.3.585

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DOI： 10.1103/PhysRevD.77.032003

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The Hard X-ray Imager (HXI) is one of three focal plane detectors on board the NeXT (New exploration X-ray Telescope) mission, which is scheduled to be launched in 2013. By use of the hybrid structure composed of double-sided silicon strip detectors and a cadmium telluride strip detector, it fully covers the energy range of photons collected with the hard X-ray telescope up to 80 keV with a high quantum efficiency. High spatial resolutions of 400 micron pitch and energy resolutions of 1-2 keV (FWMH) are at the same time achieved with low noise front-end ASICs. In addition, thick BGO active shields compactly surrounding the main detection part, as a heritage of the successful performance of the Hard X-ray Detector (HXD) on board Suzaku satellite, enable to achive an extremely high background reduction for the cosmic-ray particle background and in-orbit activation. The current status of hardware development including the design requirement, expected performance, and technical readinesses of key technologies are summarized.

DOI： 10.1117/12.788290

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

A report is made on a comprehensive observation of a burstlike gamma-ray emission from thunderclouds on the Sea of Japan, during strong thunderstorms on 6 January 2007. The detected emission, lasting for similar to 40 sec, preceded cloud-to-ground lightning discharges. The burst spectrum, extending to 10 MeV, can be interpreted as consisting of bremsstrahlung photons originating from relativistic electrons. This ground-based observation provides the first clear evidence that strong electric fields in thunderclouds can continuously accelerate electrons beyond 10 MeV prior to lightning discharges.

DOI： 10.1103/PhysRevLett.99.165002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600keV, energy resolutions of similar to 4 keV (FWHM) at 40 keV and similar to 11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.

DOI： 10.1093/pasj/59.sp1.S53

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50keV band, roughly described by an optically thick-disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above similar to 20 keV. The disk temperature decreases from 1.4 keV to 1.2 keV as the flux decreases by a factor of 2, consistent with a constant radius, as expected for disk-dominated spectra. All of the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron K alpha's at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of similar to 1000 km s(-1). The H-like iron K alpha equivalent width remains approximately constant at similar to 30 eV over all of the observations, while that of the He-like Ka line increases from 7 eV to 20 eV. Thus, the ionization state of the material decreases, as expected from the decline in flux. By fitting the profile with Voigt functions (curve of growth) together with detailed photo-ionization calculations, the total absorbing column, and the ionization parameter were estimated to be (1.0-0.7) x 10(23) cm(-2) and (6-4) x 10(4), respectively, for a velocity dispersion of 500 km s(-1). This in turn constrains the size of the plasma to be similar to 10(10) cm, assuming a source distance of 10 kpc.

DOI： 10.1093/pasj/59.sp1.S185

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Language：English   Publishing type：Research paper (international conference proceedings)  

We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630472 during its decline from its most recent outburst in 2006. All observations show the typical high/soft state spectral shape in the 250 keV band, roughly described by an optically thick disk spectrum in the soft energy band plus a weak power-law tail. The disk temperature decreases from 1.4 keV to 1.2 keV as the flux decreases by a factor 2, consistent with a constant radius as expected for disk-dominated spectra. All the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron K at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of 1000 km s 1. The Hlike iron K equivalent width remains approximately constant at 30 eV over all the observations, while that of the Helike K line increases from 7 eV to 20 eV. Thus the ionization state of the material decreases, as expected from the decline in flux. The data constrain the velocity dispersion of the absorber to 2002000 km s 1, and the size of the plasma as 10 10 cm assuming a source distance of 10 kpc. © 2007 International Astronomical Union.

DOI： 10.1017/S1743921307004620

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DOI： 10.11316/jpsgaiyo.74.2.0_535

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DOI： 10.14862/geochemproc.66.0_43

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DOI： 10.14862/geochemproc.66.0_44

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The ASTRO-H mission was designed and developed through an international collaboration of JAXA, NASA, ESA, and the CSA. It was successfully launched on February 17, 2016, and then named Hitomi. During the in-orbit verification phase, the on-board observational instruments functioned as expected. The intricate coolant and refrigeration systems for soft X-ray spectrometer (SXS, a quantum micro-calorimeter) and soft X-ray imager (SXI, an X-ray CCD) also functioned as expected. However, on March 26, 2016, operations were prematurely terminated by a series of abnormal events and mishaps triggered by the attitude control system. These errors led to a fatal event: the loss of the solar panels on the Hitomi mission. The X-ray Astronomy Recovery Mission (or, XARM) is proposed to regain the key scientific advances anticipated by the international collaboration behind Hitomi. XARM will recover this science in the shortest time possible by focusing on one of the main science goals of Hitomi, "Resolving astrophysical problems by precise high-resolution X-ray spectroscopy".(1) This decision was reached after evaluating the performance of the instruments aboard Hitomi and the mission's initial scientific results, and considering the landscape of planned international X-ray astrophysics missions in 2020's and 2030's.Hitomi opened the door to high-resolution spectroscopy in the X-ray universe. It revealed a number of discrepancies between new observational results and prior theoretical predictions. Yet, the resolution pioneered by Hitomi is also the key to answering these and other fundamental questions. The high spectral resolution realized by XARM will not offer mere refinements; rather, it will enable qualitative leaps in astrophysics and plasma physics. XARM has therefore been given a broad scientific charge: "Revealing material circulation and energy transfer in cosmic plasmas and elucidating evolution of cosmic structures and objects". To fulfill this charge, four categories of science objectives that were defined for Hitomi will also be pursued by XARM; these include (1) Structure formation of the Universe and evolution of clusters of galaxies; (2) Circulation history of baryonic matters in the Universe; (3) Transport and circulation of energy in the Universe; (4) New science with unprecedented high resolution X-ray spectroscopy. In order to achieve these scientific objectives, XARM will carry a 6 x 6 pixelized X-ray micro-calorimeter on the focal plane of an X-ray mirror assembly, and an aligned X-ray CCD camera covering the same energy band and a wider field of view. This paper introduces the science objectives, mission concept, and observing plan of XARM.

DOI： 10.1117/12.2309455

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The Astro-H (Hitomi) Soft X-ray Spectrometer (SXS) was a pioneering imaging x-ray spectrometer with 5 eV energy resolution at 6 keV. The instrument used a microcalorimeter array at the focus of a high-throughput soft x-ray telescope to enable high-resolution non-dispersive spectroscopy in the soft x-ray waveband (0 : 3 12 keV). We present the suite of ground calibration measurements acquired from 2012{2015, including characterization of the detector system, anti-coincidence detector, optical blocking filters, and filter-wheel filters. The calibration of the 36-pixel silicon thermistor microcalorimeter array includes parameterizations of the energy gain scale and line spread function for each event grade over a range of instrument operating conditions, as well as quantum efficiency measurements. The x-ray transmission of the set of five Al/polyimide thin-film optical blocking filters mounted inside the SXS dewar has been modeled based on measurements at synchrotron beamlines, including with high spectral resolution at the C, N, O, and Al K-edges. In addition, we present the x-ray transmission of the dewar gate valve and of the filters mounted on the SXS filter wheel (external to the dewar), including beryllium, polyimide, and neutral density filters.

DOI： 10.1117/12.2233053

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DOI： 10.11316/jpsgaiyo.70.2.0_358

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DOI： 10.11316/jpsgaiyo.70.1.0_470

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DOI： 10.11316/jpsgaiyo.70.1.0_259

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We present the results of six Suzaku observations of the recurrent black hole transient 4U 1630-472 during its decline from its most recent outburst in 2006. All observations show the typical high/soft state spectral shape in the 2-50 keV band, roughly described by an optically thick disk spectrum in the soft energy band plus a weak power-law tail. The disk temperature decreases from 1.4 keV to 1.2 keV as the flux decreases by a factor 2, consistent with a constant radius as expected for disk-dominated spectra. All the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron K alpha at 7.0 keV and 6.7 keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of similar to 1000 km s(-1). The H-like iron K alpha equivalent width remains approximately constant at similar to 30 eV over all the observations, while that of the He-like K alpha line increases from 7 eV to 20 eV. Thus the ionization state of the material decreases, as expected from the decline in flux. The data constrain the velocity dispersion of the absorber to 200-2000 km s(-1) and the size of the plasma as similar to 10(10) cm assuming a source distance of 10 kpc.

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