研究者業績
基本情報
- 所属
- 埼玉大学大学院 理工学研究科 教授国立研究開発法人宇宙航空研究開発機構 宇宙科学研究所 特任教授
- 学位
- 修士（理学）(東京大学)博士（理学）(東京大学)
- J-GLOBAL ID
- 200901083726265608
- researchmap会員ID
- 1000161587
- 外部リンク
研究キーワード
14学歴
6-
- 1993年
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- 1990年
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- 1988年
委員歴
2-
2020年11月 - 現在
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2009年1月 - 2013年5月
受賞
4-
2007年
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2007年
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1999年
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1999年
論文
165-
Publications of the Astronomical Society of Japan 65(4) 2013年8月25日 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 65(4) 74-1-11 2013年8月25日 査読有り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 < 2.54. Taking into account a flux variation o
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 207(2) 2013年8月 査読有りWe present Interplanetary Network (IPN) data for the gamma-ray bursts in the first Fermi Gamma-Ray Burst Monitor (GBM) catalog. Of the 491 bursts in that catalog, covering 2008 July 12 to 2010 July 11, 427 were observed by at least one other instrument in the nine-spacecraft IPN. Of the 427, the localizations of 149 could be improved by arrival time analysis (or "triangulation"). For any given burst observed by the GBM and one other distant spacecraft, triangulation gives an annulus of possible arrival directions whose half-width varies between about 0.'4 and 32 degrees, depending on the intensity, time history, and arrival direction of the burst, as well as the distance between the spacecraft. We find that the IPN localizations intersect the 1 sigma GBM error circles in only 52% of the cases, if no systematic uncertainty is assumed for the latter. If a 6 degrees systematic uncertainty is assumed and added in quadrature, the two localization samples agree about 87% of the time, as would be expected. If we then multiply the resulting error radii by a factor of three, the two samples agree in slightly over 98% of the cases, providing a good estimate of the GBM 3 sigma error radius. The IPN 3 sigma error boxes have areas between about 1 arcmin(2) and 110 deg(2), and are, on the average, a factor of 180 smaller than the corresponding GBM localizations. We identify two bursts in the IPN/GBM sample that did not appear in the GBM catalog. In one case, the GBM triggered on a terrestrial gamma flash, and in the other, its origin was given as "uncertain." We also discuss the sensitivity and calibration of the IPN.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 65(4) 2013年8月 査読有りTo search for possible non-thermal emissions from magnetic white dwarfs (WDs), we selected the most suitable candidates from among magnetic cataclysmic variables and isolated WDs. After the magnetic cataclysmic variable AE Aquarii, which emits hard X-ray pulses, the isolated WD EUVE J0317-855 is expected to emit the second most powerful magnetic dipole radiation with energies reaching similar to 1.1 x 10(29) erg s(-1). EUVE J0317-855 was observed with Suzaku from 2009 July 16 to 2009 July 17 for about 60 ks. No significant emissions were detected from the object in the 0.5-10 keV band, and the upper limit of the X-ray flux was estimated to be 1.7 x 10(-13) erg cm(-2) s(-1) in the 2-10 keV band. This value corresponds to less than 0.05% of the calculated spin-down energy. It excludes the possibility of explaining soft gamma-ray repeaters and anomalous X-ray pulsars as WDs, but may indicate that the activity in the magnetosphere of WDs is not so different from that occurring in radio pulsars. Curvature radiation, which is one of the suggested mechanism for emissions from the magnetosphere of compact objects, may explain the observed X-ray flux of AE Aquarii, and is consistent with the non-detection of EUVE J0317-855.
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EXPERIMENTAL ASTRONOMY 34(2) 519-549 2012年10月ORIGIN is a proposal for the M3 mission call of ESA aimed at the study of metal creation from the epoch of cosmic dawn. Using high-spectral resolution in the soft X-ray band, ORIGIN will be able to identify the physical conditions of all abundant elements between C and Ni to red-shifts of z = 10, and beyond. The mission will answer questions such as: When were the first metals created? How does the cosmic metal content evolve? Where do most of the metals reside in the Universe? What is the role of metals in structure formation and evolution? To reach out to the early Universe ORIGIN will use Gamma-Ray Bursts (GRBs) to study their local environments in their host galaxies. This requires the capability to slew the satellite in less than a minute to the GRB location. By studying the chemical composition and properties of clusters of galaxies we can extend the range of exploration to lower redshifts (z similar to 0.2). For this task we need a high-resolution spectral imaging instrument with a large field of view. Using the same instrument, we can also study the so far only partially detected baryons in the Warm-Hot Intergalactic Medium (WHIM). The less dense part of the WHIM will be studied using absorption lines at low redshift in the spectra for GRBs. The ORIGIN mission includes a Transient Event Detector (coded mask with a sensitivity of 0.4 photon/cm(2)/s in 10 s in the 5-150 keV band) to identify and localize 2000 GRBs over a five year mission, of which similar to 65 GRBs have a redshift > 7. The Cryogenic Imaging Spectrometer, with a spectral resolution of 2.5 eV, a field of view of 30 arcmin and large effective area below 1 keV has the sensitivity to study clusters up to a significant fraction of the virial radius and to map the denser parts of the WHIM (factor 30 higher than achievable with current instruments). The payload is complemented by a Burst InfraRed Telescope to enable onboard red-shift determination of GRBs (hence securing proper follow up of high-z bursts) and also probes the mildly ionized state of the gas. Fast repointing is achieved by a dedicated Controlled Momentum Gyro and a low background is achieved by the selected low Earth orbit.
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ASTROPHYSICAL JOURNAL 751(2) 2012年6月 査読有りWe present a generalized analytic formalism for the inverse Compton X-ray emission from hydrogen-poor supernovae and apply this framework to SN 2011fe using Swift X-Ray Telescope (XRT), UVOT, and Chandra observations. We characterize the optical properties of SN 2011fe in the Swift bands and find them to be broadly consistent with a "normal" SN Ia, however, no X-ray source is detected by either XRT or Chandra. We constrain the progenitor system mass-loss rate (M) over dot < 2 x 10(-9) M-circle dot yr(-1) (3 sigma c.l.) for wind velocity v(w) = 100 km s(-1). Our result rules out symbiotic binary progenitors for SN 2011fe and argues against Roche lobe overflowing subgiants and main-sequence secondary stars if greater than or similar to 1% of the transferred mass is lost at the Lagrangian points. Regardless of the density profile, the X-ray non-detections are suggestive of a clean environment (n(CSM) < 150 cm(-3)) for 2 x 10(15) less than or similar to R less than or similar to 5 x 10(16) cm around the progenitor site. This is either consistent with the bulk of material being confined within the binary system or with a significant delay between mass loss and supernova explosion. We furthermore combine X-ray and radio limits from Chomiuk et al. to constrain the post-shock energy density in magnetic fields. Finally, we searched for the shock breakout pulse using gamma-ray observations from the Interplanetary Network and find no compelling evidence for a supernova-associated burst. Based on the compact radius of the progenitor star we estimate that the shock breakout pulse was likely not detectable by current satellites.
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JOURNAL OF LOW TEMPERATURE PHYSICS 167(5-6) 795-802 2012年6月 査読有り
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AIP Conference Proceedings 1427 265-266 2012年5月10日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 w ith 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.
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ASTROPHYSICAL JOURNAL 751(1) 35 2012年5月 査読有り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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 64(2) 2012年4月 査読有りThis paper presents a study on the spectral evolution of gamma-ray burst (GRB) prompt emissions observed with the Suzaku Wide-band All-sky Monitor (WAM). By making use of the WAM data archive, 6 bright GRBs exhibiting 7 well-separated fast-rise-exponential-decay (FRED) shaped light curves are presented, and the evaluated exponential decay time constants of the energy-resolved light curves from these FRED peak light curves are shown to indicate significant spectral evolution. The energy dependence of the time constants is well described with a power-law function, tau(E) alpha E-gamma, where gamma similar to -(0.34 +/- 0.12) on average, although 5 FRED peaks show a consistent value of gamma = -1/2, which is expected in synchrotron or inverse-Compton cooling models. In particular, 2 of the GRBs were located with accuracy sufficient to evaluate the time-resolved spectra with precise energy response matrices. Their behavior in spectral evolution suggests two different origins of emissions. In the case of GRB 081224, the derived 1-s time-resolved spectra are well described by a blackbody radiation model with a power-law component. The derived behavior of cooling is consistent with that expected from radiative cooling or expansion of the emission region. On the other hand, the other 1-s time-resolved spectra from GRB 100707A is well described by a Band GRB model as well as with the thermal model. Although relative poor statistics prevent us to conclude, the energy dependence in the decaying light curve is consistent with that expected in the former emission mechanism model.
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ASTROPHYSICAL JOURNAL LETTERS 748(1) 2012年3月 査読有りThis study presents multi-wavelength observational results for energetic GRB 100414A with GeV photons. The prompt spectral fitting using Suzaku/WAM data yielded spectral peak energies of E-peak(src) of 1458.7(-106.6)(+132.6) keV and E-iso of 34.5(-1.8)(+2.0) x 10(52) erg with z = 1.368. The optical afterglow light curves between 3 and 7 days were effectively fitted according to a simple power law with a temporal index of alpha = -2.6 +/- 0.1. The joint light curve with earlier Swift/UVOT observations yields a temporal break at 2.3 +/- 0.2 days. This was the first Fermi/LAT detected event that demonstrated the clear temporal break in the optical afterglow. The jet opening angle derived from this temporal break was 5 degrees.8, consistent with those of other well-observed long gamma-ray bursts (GRBs). The multi-wavelength analyses in this study showed that GRB 100414A follows E-peak(src)-E-iso and E-peak(src)-E-gamma correlations. The late afterglow revealed a flatter evolution with significant excesses at 27.2 days. The most straightforward explanation for the excess is that GRB 100414A was accompanied by a contemporaneous supernova. The model light curve based on other GRB-SN events is marginally consistent with that of the observed light curve.
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Publications of the Astronomical Society of Japan 64(1) 2012年2月25日 査読有り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.
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りSearching for new types of particle-acceleration sites is important. Recently, Synchrotron emission has been reported from a bow shock region from a runway star BD+43 degrees 3654 with a radio observation by VLA. It was the first discovery of a non-thermal emission from a runaway star. In order to search for possible non-thermal tail in the X-ray band, we have performed the observation of the object BD+43 degrees 3654 with Suzaku in April 2011 with the exposure of 105 ksec. As a result, thanks to the stable low-background capability of the XIS, we detected X-rays around the bow shock region. The X-ray luminosity of the diffuse X-rays around the object was about 10(31) erg s(-1) in the 0.5 to 10 keV band. In addition, we also detected X-rays from the object itself, BD+43 degrees 3654, representing a thermal X-ray spectrum with a temperature of 0.6 keV at the luminosity of 1.3x10(31) erg s(-1) in the same band. Detail analyses will be reported in a future paper. The results suggest the conversion efficiency from the momentum of the stellar wind into accelerated electrons would be the same order of magnitudes of those seen in shocks of supernova remnants.
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SPACE TELESCOPES AND INSTRUMENTATION 2012: ULTRAVIOLET TO GAMMA RAY 8443 844326-19pp 2012年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.
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IEEE Nuclear Science Symposium Conference Record 163-166 2012年 査読有りASTRO-H is an X-ray astronomy satellite to be launched in 2014. The data acquisition system of this mission is realized with a standard network protocol, SpaceWire. Although the protocol itself is well designed, a new concept to grantee the quality of service will be installed to the ASTRO-H data acquisition system. Therefore, the verification of the design of the concept is essential in the initial phase of the development. The time assignment function is one of the important issues for the SpaceWire development. The accuracy of the absolute time of about 30 μs is required from science goals. The key point of the time assignment with SpaceWire network in the ASTRO-H system is how accurately sharing the time information. In this paper, our design of the time distribution and assignment system for ASTRO-H is shown. The results of our measurements of timing accuracy are also presented to show that the design will fulfill the goal of absolute timing accuracy. © 2011 IEEE.
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りSuzaku observations are reported of the three giant radio galaxies, 3C 35, 3C 326, and DA 240, with a projected linear size of greater than or similar to 1 Mpc. The low and stable instrumental background of the X-ray Imaging Spectrometer onboard Suzaku allows a significant detection of inverse Compton X-ray emission from the lobes of these giant radio galaxies. As a result, the electron and magnetic energy densities in the lobes were measured. Based on the measurements, the late phase in the evolution of the energetics associated with jets from active galactic nuclei was investigated. It is found that the lobes of giant radio galaxies tend to reside in a near equipartition condition between electrons and magnetic field, despite the fact that smaller sources with sizes of about 100 kpc exhibit a particle dominance by a typical factor of 10 in energy density. In addition, the energy densities in the giant lobes are measured to be smaller by an order of magnitude as compared to the extrapolation of the size to energy density correlation found for smaller radio galaxies. These results indicate that typical radio galaxies experience a significant reduction in their jet power, as their jets evolve in size from 100 kpc to 1 Mpc.
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SUZAKU 2011: EXPLORING THE X-RAY UNIVERSE: SUZAKU AND BEYOND 1427 2012年 査読有りThe BGO anticoincidence shield of the Suzaku Hard X-Ray Detector Wideband All-Sky Monitor (HXD WAM) has been designed to act as a gamma-ray burst detector. It was incorporated into the 3rd interplanetary network shortly after launch, and it is now detecting about one confirmed gamma-ray or soft gamma repeater burst every 2.5 days. It has detected almost 900 events so far.
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DEATH OF MASSIVE STARS: SUPERNOVAE AND GAMMA-RAY BURSTS (279) 411-412 2012年 査読有りAn observational study is presented of the spectral evolution of gamma-ray burst (GRB) prompt emissions with the Suzaku Wide-band All-sky Monitor (WAM). We selected 6 bright GRBs exhibiting 7 well-separated fast-rise-exponential-decay (FRED) shaped light curves to investigate spectral changes by evaluating exponential decay time constants of the energy resolved light curves. In addition, we carried out time-resolved spectroscopy of two of them which were located with accuracy sufficient to evaluate the time-resolved spectra with precise energy response matrices. The two imply different emission mechanisms; the one is well reproduced with a cooling blackbody radiation model with a power-law component, while the other prefers non-thermal emission model with a decaying turn over energy.
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SPACE TELESCOPES AND INSTRUMENTATION 2012: ULTRAVIOLET TO GAMMA RAY 8443 2012年 査読有り
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ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES 197(2) 2011年12月 査読有りBetween 2000 November and 2006 May, one or more spacecraft of the interplanetary network (IPN) detected 226 cosmic gamma-ray bursts that were also detected by the French Gamma-Ray Telescope experiment on board the High Energy Transient Experiment 2 spacecraft. During this period, the IPN consisted of up to nine spacecraft, and using triangulation, the localizations of 157 bursts were obtained. We present the IPN localization data on these events.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(SPEC. ISSUE 3) S645-S656 2011年11月25日 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63 S947-S955 2011年11月 査読有りA careful analysis of the Suzaku data of the giant radio galaxy DA 240, of which the size is 1.48 Mpc, revealed diffuse X-ray emission associated with its east lobe. The diffuse X-ray spectrum was described with a simple power-law model with a photon index of Gamma = 1.92(-0.17-0.06)(+0.13+0.04) where the first and second errors represent the statistical and systematic ones. The agreement with the synchrotron radio photon index, Gamma(R) = 1.95 +/- 0.01 in 326-608.5 MHz, ensures that any excess X-ray emission is attributed to inverse Compton emission from the synchrotron-radiating electrons, boosting up the cosmic microwave background photons. From the X-ray flux density, 51.5 +/- 3.91(-5.4)(+6.2) nJy at 1 keV, derived with the photon index fixed at Gamma(R), in comparison with the synchrotron radio intensity of 10.30 +/- 0.12 Jy at 326 MHz, the magnetic and electron energy densities were estimated as u(m) = (3.0 +/- 0.2 +/- 0.4) x 10(-14)erg cm(-3) and u(e) =(34(-0.2-0.4)(+0.3+0.5)) x 10(-14)erg cm(-3) integrated over the electron Lorentz factor of 10(3)-10(5), respectively. Thus, the east lobe is found to reside in an equipartition condition between the electrons and magnetic field parametrized as u(e)/u(m) = 1.1(-0.1-0.2)(+0.2+0.4). The east lobe of DA 240 is indicated to exhibit the lowest value of tie, among all of the X-ray detected lobes of radio galaxies. A comparison of the energetics in the giant radio galaxies with a size of 1 Mpc to those in the smaller objects suggests a possibility that radio galaxies lose their jet power as they evolve from similar to 100 kpc to similar to 1 Mpc.
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Astrophysical Journal Letters 734(2) 2011年6月20日 査読有りSoft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely 1kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0-5408, gave a burst with an estimated isotropic energy > 1044erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band- and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090Hz), are 3.0 × 1044 d 2 1erg and 1.4 × 10 47 d 2 1erg, respectively, where and d 0501 is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time. © 2011. The American Astronomical Society. All rights reserved.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(1) 215-277 2011年2月 査読有りWe report on the spectral cross-calibration results of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed gamma-ray bursts (GRBs). This is the first attempt to use simultaneously observed GRBs as a spectral calibration source to understand systematic problems among the instruments. Based on these joint spectral fits, we find that (1) although a constant factor (a normalization factor) agrees within 20% among the instruments, the BAT constant factor shows a systematically smaller value by 10%-20% compared to that of Konus-Wind, (2) there is a systematic trend that the low-energy photon index becomes steeper by 0.1-0.2 and E-peak becomes systematically higher by 10%-20% when including the BAT data in the joint fits, and (3) the high-energy photon index agrees within 0.2 among the instruments. Our results show that cross-calibration based on joint spectral analysis is an important step to understanding the instrumental effects that could be affecting the scientific results from the GRB prompt emission data.
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ASTROPHYSICAL JOURNAL 727(2) 2011年2月 査読有りThe Suzaku observation of a giant radio galaxy 3C 35 revealed faint extended X-ray emission, associated with its radio lobes and/or host galaxy. After careful subtraction of the X-ray and non-X-ray background and contaminating X-ray sources, the X-ray spectrum of the faint emission was reproduced by a sum of the power-law (PL) and soft thermal components. The soft component was attributed to the thermal plasma emission from the host galaxy. The photon index of the PL component, Gamma = 1.35(-0.86-0.10)(+0.56+0.11),where the first and second errors represent the statistical and systematic ones, was found to agree with the synchrotron radio index from the lobes, Gamma(R) = 1.7. Thus, the PL component was attributed to the inverse Compton (IC) X-rays from the synchrotron electrons in the lobes. The X-ray flux density at 1 keV was derived as 13.6 +/- 5.4(-3.6)(+4.0) nJy with the photon index fixed at the radio value. The X-ray surface brightness from these lobes (similar to 0.2 nJy arcmin(-2)) is lowest among the lobes studied through the IC X-ray emission. In combination with the synchrotron radio flux density, 7.5 +/- 0.2 Jy at 327.4 MHz, the electron energy density spatially averaged over the lobes was evaluated to be the lowest among those radio galaxies, as u(e) = (5.8 +/- 2.3(-1.7)(+1.9)) x 10(-14) erg cm(-3) over the electron Lorentz factor of 10(3) - 10(5). The magnetic energy density was calculated as u(m) = (3.1(-1.0-0.9)(+2.5+1.4)) x 10(-14) erg cm(-3), corresponding to the magnetic field strength of 0.88(-0.16-0.14)(+0.31+0.19) mu G. These results suggest that the energetics in the 3C 35 lobes are nearly consistent with equipartition between the electrons and magnetic fields.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 63(1) 137-146 2011年2月 査読有りThe WIDeField telescope for Gamma-ray burst Early Timing (WIDGET) is used for a fully automated, ultrawide-field survey aimed at detecting the prompt optical emission associated with Gamma-ray Bursts (GRBs). WIDGET surveys the HETE-2 and Swift/BAT pointing directions, covering a total field of view of 62 x 62 every 10 secounds using a unfiltered system. This monitoring survey allows the exploration of optical emission before the gamma-ray trigger. The unfiltered magnitude is well converted to the SDSS r' system at a 0.1 mag level. Since 2004, WIDGET has made a total of ten simultaneous and one pre-trigger GRB observations. The efficiency of synchronized observations with HETE-2 is four-times better than that of Swift. There has been no bright optical emission similar to that from GRB 080319B. A statistical analysis implies that GRB 080319B is a rare event. This paper summarizes the design and operation of the WIDGET system and the simultaneous GRB observations obtained with this instrument.
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AIP Conference Proceedings 1358 385-388 2011年 査読有りThe 3rd interplanetary network (IPN), which has been in operation since 1990, presently consists of 9 spacecraft: AGILE, Fermi, RHESSI, Suzaku, and Swift, in low Earth orbit INTEGRAL, in eccentric Earth orbit with apogee 0.5 light-seconds Wind, up to ∼7 light-seconds from Earth MESSENGER, en route to Mercury and Mars Odyssey, in orbit around Mars. The IPN operates as a full-time, all-sky monitor for transients down to a threshold of about 6×10-7 erg cm-2 or 1 photon cm-2 s-1. It detects ∼335 cosmic gamma-ray bursts per year. These events are generally not the same ones detected by narrower field of view instruments such as Swift, INTEGRAL IBIS, SuperAGILE, and MAXI the localization accuracy is in the several arcminute and above range. The data are publicly available and can be utilized for a wide variety of studies. © 2011 American Institute of Physics.
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JETS AT ALL SCALES (275) 184-185 2011年 査読有りWe performed mapping observations of the Fornax A west lobe with Suzaku in order to measure X-ray brightness distribution. Thanks to the low and stable background of Suzaku, we succeeded in detecting the faint diffuse X-ray emission from the west lobe. Performing careful corrections to the obtained images, we finally measured the X-ray brightness profile extending over the lobe. By comparing the X-ray and radio profiles, the magnetic field found to be fairly constant at similar to 1 mu G over the lobe, while the electron energy distribution is suggested to concentrate on the lobe center.
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2011 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (NSS/MIC) 163-166 2011年 査読有りASTRO-H is an X-ray astronomy satellite to be launched in 2014. The data acquisition system of this mission is realized with a standard network protocol, SpaceWire. Although the protocol itself is well designed, a new concept to grantee the quality of service will be installed to the ASTRO-H data acquisition system. Therefore, the verification of the design of the concept is essential in the initial phase of the development. The time assignment function is one of the important issues for the SpaceWire development. The accuracy of the absolute time of about 30 mu s is required from science goals. The key point of the time assignment with SpaceWire network in the ASTRO-H system is how accurately sharing the time information. In this paper, our design of the time distribution and assignment system for ASTRO-H is shown. The results of our measurements of timing accuracy are also presented to show that the design will fulfill the goal of absolute timing accuracy.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(6) 1435-1443 2010年12月 査読有りThe Suzaku X-ray satellite observed the nearby S0 galaxy NGC 1316, a merger remnant aged 3 Gyr. The total good exposure time was 48.7 ks. The spectra were well represented by a two-temperature thermal model for the interstellar medium (ISM) plus a power-law model. The cool and hot temperatures of the thermal model were 0.48 +/- 0.03 and 0.92 +/- 0.04 keV, respectively. The excellent spectral sensitivity of Suzaku enables us for the first time to measure the metal abundances of O, Ne, Mg, Si, and Fe in the ISM. The resultant abundance pattern of O, Ne, Mg, Si, and Fe is close to that of the new solar abundance determined by Lodders (2003, ApJ, 591, 1220). The measured abundance pattern is compared with those of elliptical galaxies and an S0 galaxy, observed with Suzaku. Considering metal-enrichment from present Type la supernovae, the near-solar abundance pattern of the ISM in NGC 1316 indicates an enhanced alpha/Fe ratio of stellar materials in the entire galaxy, like in giant elliptical galaxies.
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Proceedings of SPIE - The International Society for Optical Engineering 7732 2010年10月19日We present the science and an overview of the Soft X-ray Spectrometer onboard the ASTRO-H mission with emphasis on the detector system. The SXS consists of X-ray focusing mirrors and a microcalorimeter array and is developed by international collaboration lead by JAXA and NASA with European participation. The detector is a 6×6 format microcalorimeter array operated at a cryogenic temperature of 50 mK and covers a 3′ ×3′ filed of view of the X-ray telescope of 5.6 m focal length. We expect an energy resolution better than 7 eV (FWHM, requirement) with a goal of 4 eV. The effective area of the instrument will be 225 cm2 at 7 keV; by a factor of about two larger than that of the X-ray microcalorimeter on board Suzaku. One of the main scientific objectives of the SXS is to investigate turbulent and/or macroscopic motions of hot gas in clusters of galaxies. © 2010 SPIE.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(5) 1341-1349 2010年10月 査読有りWe developed a catalog of solar flares in the hard X-ray band observed with the Wide-band All-sky Monitor (WAM) onboard the Suzaku satellite between 2005 July and 2009 November. During this period, 105 solar flares (GOES class X: 13, M: 29, C: 47, B: 16) were detected with WAM, including 10% of GOES-class C events reported during the same period. The observed photon flux ranged between 9 x 10(-5) and 9 x 10(-1) photons s(-1) cm(-2) keV(-1) at 100 keV. The averaged hard X-ray spectrum for each solar flare was evaluated for 70 of the 105 events, and 43 of them were well fitted with a single power-law model with a photon index ranging between -7 and -3. We observed a weak trend where events with longer durations exhibited harder spectral slopes.
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The Astrophysical Journal 714(1) 37-44 2010年5月1日 査読有りUsing deep Chandra Advanced CCD Imaging Spectrometer (ACIS) observation data for Cygnus A, we report evidence of non-thermal X-ray emission from radio lobes surrounded by a rich intracluster medium (ICM). The diffuse X-ray emission, which is associated with the eastern and western radio lobes, was observed in a 0.7-7 keV Chandra ACIS image. The lobe spectra are reproduced with not only a single-temperature Mekal model, such as that of the surrounding ICM component, but also an additional power-law (PL) model. The X-ray flux densities of PL components for the eastern and western lobes at 1 keV are derived as 77.7+28.9 -31.9 nJy and 52.4+42.9 -42.4 nJy, respectively, and the photon indices are 1.69 +0.07 -0.13 and 1.84+2.90 -0.12, respectively. The non-thermal component is considered to be produced via the inverse Compton (IC) process, as is often seen in the X-ray emission from radio lobes. From a re-analysis of radio observation data, the multiwavelength spectra strongly suggest that the seed photon source of the IC X-rays includes both cosmic microwave background radiation and synchrotron radiation from the lobes. The derived parameters indicate significant dominance of the electron energy density over the magnetic field energy density in the Cygnus A lobes under the rich ICM environment. © 2010. The American Astronomical Society. All rights reserved..
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AIP Conference Proceedings 1279 89-92 2010年 査読有りA result of a joint timing analysis is presented for prompt emission of long-duration (T90 = 81 s) GRB 090709A with Swift Burst Alert Telescope (Swift/BAT), Suzaku Wide-band All-sky Monitor (Suzaku/WAM) and Konus-Wind over an energy range from 15 keV to 5 MeV. It was reported that multi-peaked GRB 090709A exhibited a possible periodic behavior with a period of about 8 s which is comparable to typical time scale of soft gamma-ray repeaters. However, the periodicity is still marginal in detailed analysis with Swift/BAT and GRB090709A exhibited a typical afterglow [1] [2]. To investigate significance of the periodicity more quantitatively, we performed a detailed timing analysis on all the lightcurves obtained with Suzaku/WAM, Swift/BAT, and Konus-Wind evaluating their underlying trend, red noise and white noise. © 2010 American Institute of Physics.
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SPACE TELESCOPES AND INSTRUMENTATION 2010: ULTRAVIOLET TO GAMMA RAY 7732 2010年 査読有り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 (40-600 keV) at a background level 10 times better than the current instruments on orbit. 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. The ASTRO-H mission is approved by ISAS/JAXA to proceed to a detailed design phase with an expected launch in 2014. In this paper, we present science drivers and concept of the SGD instrument followed by detailed description of the instrument and expected performance.
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AIP Conference Proceedings 1279 330-333 2010年 査読有りThe 3rd interplanetary network (IPN), which has been in operation since 1990, presently consists of 9 spacecraft: AGILE, Fermi, RHESSI, Suzaku, and Swift, in low Earth orbit INTEGRAL, in eccentric Earth orbit with apogee 0.5 light-seconds Wind, up to ∼7 light-seconds from Earth MESSENGER, en route to Mercury and Mars Odyssey, in orbit around Mars. The IPN operates as a full-time, all-sky monitor for transients down to a threshold of about 6 × 10-7 erg cm-2 or 1 photoncm-2 s-1. It detects ∼346 cosmic gamma-ray bursts per year. These events are generally not the same ones detected by narrower field of view instruments such as Swift, INTEGRAL IBIS, and SuperAGILE the localization accuracy is in the several arcminute and above range. The uses of the IPN data are described. © 2010 American Institute of Physics.
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Proceedings of SPIE - The International Society for Optical Engineering 7732 2010年 査読有りThe Soft X-ray Spectrometer (SXS) instrument on the Astro-H observatory is based on a 36 pixel x-ray calorimeter array cooled to 50 mK in a sophisticated spaceflight cryostat. The SXS is a true spatial-spectral instrument, where each spatially discrete pixel functions as a high-resolution spectrometer. Here we discuss the SXS detector subsystem that includes the detector array, the anticoincidence detector, the first stage amplifiers, the thermal and mechanical staging of the detector, and the cryogenic bias electronics. The design of the SXS detector subsystem has significant heritage from the Suzaku/XRS instrument but has some important modifications that increase performance margins and simplify the focal plane assembly. Notable improvements include x-ray absorbers with significantly lower heat capacity, improved load resistors, improved thermometry, and a decreased sensitivity to thermal radiation. These modifications have yielded an energy resolution of 3.5-4.0 eV FWHM at 6 keV for representative devices in the laboratory, giving considerable margin against the 7 eV instrument requirement. We expect similar performance in flight. © 2010 SPIE.
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DECIPHERING THE ANCIENT UNIVERSE WITH GAMMA-RAY BURSTS 1279 436-438 2010年 査読有りA study of spectral evolutions of gamma-ray burst (GRB) prompt emissions observed with Suzaku Wide-band All-sky Monitor (WAM) is presented. Thank to the large effective areas, Suzaku-WAM is one of the best instruments to investigate spectral evolutions of the ORB prompt emissions. In general the rise and decay time scales in the light curves are determined by the heating and cooling time scale and geometrical effect of the emission regions. It has been argued that the expected highly relativistic emission regions and its deceleration would produce spectral evolution could cause apparent spectral evolution in the observer frame. However, it is not easy to attribute exponential decays with spectral evolutions to the relativistic effect of the GRB jet. In other words, electron cooling is the key to solve the spectral variations in the exponential decays. This paper focuses the isolated fast-rise-exponential-decay (FRED) type light curve observed with WAM and their spectral evolutions, and revealed an energy dependence of the time constant of the observed exponential decay. The "energy indices" observed from some of the GRBs are consistent with those expected in synchrotron or inverse Compton cooling.
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SPACE TELESCOPES AND INSTRUMENTATION 2010: ULTRAVIOLET TO GAMMA RAY 7732 2010年 査読有りOne of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) with absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The requirements for this instrument are demanding. In the central array (40 x 40 pixels) an energy resolution of <2.5 eV is required, whereas the energy resolution of the outer array is more relaxed (approximate to 10 eV) but the detection elements have to be a factor 16 larger in order to keep the number of read-out channels acceptable for a cryogenic instrument. Due to the large collection area of the IXO optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. In this paper we will summarize the instrument status and performance. We will describe the results of design studies for the focal plane assembly and the cooling systems. Also the system and its required spacecraft resources will be given.
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Proceedings of SPIE - The International Society for Optical Engineering 7732 2010年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 62(3) 547-556 2010年 査読有りTime-resolved spectral analyses of GRB 070125 with significant photon detections over the MeV regime using Suzaku/WAM data are reported. The prompt emission interval was divided into 10 time regions, and their spectra were reproduced by a Band function or a cutoff power-law model. The spectra show a complex evolution; a soft-hard-soft trend is seen, rather than a typical hard-to-soft monotonic variation. In addition, a flat spectral slope in the low-energy band exceeding the slope expected from a simple synchrotron emission model is suggested in one of the time regions. These results imply that the internal shocks in the relativistic jet of GRB 070125 have different physical conditions. There is a possible excess at similar to 2.2 MeV in the spectrum of 33 seconds after the trigger at a significant level of approximate to 98.5%, where the continuum spectrum is not reproduced by the Band function. These properties are only shown during the short prompt time interval of the prompt emission, and emphasize the utility of the Suzaku/WAM for the study of gamma-ray bursts.
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 623(1) 425-427 2010年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(3) 521-527 2009年6月 査読有りWe present the results of the high-redshift GRB 050904 at z = 6.295 from joint spectral analysis among Swift-BAT, Konus-Wind, and Suzaku-WAM, covering a wide energy range of 15-5000 keV. The nu F-nu spectrum peak energy, E-peak, was measured at 314(-89)(+173) keV, corresponding to 2291(-634)(+1263) keV in the source frame, and the isotropic equivalent radiated energy, E-iso, was estimated to be 1.04(-0.17)(+0.21) x 10(54)erg. Both are among the highest values that have ever been measured. GRBs with such a high E-iso (similar to 10(54) erg) might be associated with prompt optical emission. The derived spectral and energetic parameters are consistent with the correlation between the rest-frame E-p,E-i and the E-iso (Amati relation), but not with the correlation between the intrinsic peak energy E-p,E-i and the collimation-corrected energy E-gamma (Ghirlanda relation), unless the density of the circumburst environment of this burst is much larger than the nominal value, as suggested by other wavelength observations. We also discuss the possibility that this burst is an outlier in the correlation between E-p,E-i and the peak luminosity L-p (Yonetoku relation).
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S35-S53 2009年1月 査読有りThe Suzaku Wide-band All-sky Monitor (WAM) consists of thick BGO anti-coincidence shields of the Hard X-ray Detectors (HXD). It views about half of the sky and has a geometrical area of 800 cm(2) per side and an effective area of 400 cm(2), even at 1 MeV. Hence, the WAM can provide unique opportunities to detect high-energy emission from GRBs and solar flares in the sub-MeV to MeV range. The WAM has detected more than 400 GRBs and 100 solar flares since its launch. This paper describes the in-flight performance of the HXD/WAM during the initial two years of operations, including the in-flight energy response, spectral and timing capabilities, and in-orbit background.
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Astrophysical Journal 706(1) L183-L187 2009年 査読有りWe present multi-band results for GRB071010B based on Swift, Suzaku, and ground-based optical observations. This burst is an ideal target to evaluate the robustness of the Esrcpeak - Eiso and E srcpeak - Eγ relations, whose studies have been in stagnation due to the lack of the combined estimation of E srcpeak and long-term optical monitoring. The joint prompt spectral fitting using Swift/Burst Alert Telescope and Suzaku/Wide-band All-sky Monitor data yielded the spectral peak energy as Esrcpeak of 86.5+6.4-6.3 keV and Eiso of 2.25 +0.19-0.16 × 1052 erg with z = 0.947. The optical afterglow light curve is well fitted by a simple power law with temporal index α = -0.60 0.02. The lower limit of temporal break in the optical light curve is 9.8 days. Our multi-wavelength analysis reveals that GRB071010B follows Esrcpeak - Eiso but violates the Esrcpeak - Eγ and Eiso - Esrcpeak - tsrcjet at more than the 3σ level.
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AIP Conference Proceedings 1133 55-57 2009年 査読有りThe 3rd interplanetary network (IPN), which has been in operation since 1990, presently consists of 9 spacecraft: AGILE, RHESSI, Suzaku, and Swift, in low Earth orbit INTEGRAL, in eccentric Earth orbit with apogee 0.5 light-seconds Wind, up to ∼7 light-seconds from Earth MESSENGER, en route to Mercury and Mars Odyssey, in orbit around Mars. Ulysses and HETE have ceased operations, and the Fermi GBM is being incorporated into the network. The IPN operates as a full-time, all-sky monitor for transients down to a threshold of about 6x10-7 erg cm-2 or 1 photon cm-2 s -1. It detects about 275 cosmic gamma-ray bursts per year. These events are generally not the same ones detected by narrower field of view imaging instruments such as Swift, INTEGRAL IBIS, and SuperAGILE the localization accuracy is in the several arcminute and above range. © 2009 American Institute of Physics.
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AIP Conference Proceedings 1133 344-349 2009年 査読有りIn recent years several authors have derived correlations between gamma-ray burst (GRB) spectral peak energy (Epeak) and either isotropic-equivalent radiated energy (Eiso) or peak luminosity (Liso). Since these relationships are controversial, but could provide redshift estimators, it is important to determine whether bursts detected by Swift exhibit the same correlations. Swift has greatly added to the number of GRBs for which redshifts are known and hence Eiso and Liso could be calculated. However, for most bursts it is not possible to adequately constrain Epeak with Swift data alone since many GRBs have Epeak above the energy range (15-150 keV) of the Swift Burst Alert Telescope (BAT). Therefore we have analyzed the spectra of 78 bursts (31 with redshift) which were detected by both Swift/BAT and the Suzaku Wide-band All-sky Monitor (WAM), which covers the energy range 50-5000 keV. For most bursts in this sample we can precisely determine Epeak and for bursts with known redshift we can compare how the Epeak relations for the Swift/Suzaku sample compare to earlier published results. © 2009 American Institute of Physics.
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AIP Conference Proceedings 1133 91-93 2009年 査読有り
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Publications of the Astronomical Society of Japan 61(SUPPL. 1) 2009年 査読有り
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(5) 1011-1022 2009年 査読有りSuzaku observations of the blazar OJ 287 were performed in 2007 April 10-13 and November 7-9. They correspond to a quiescent and a flaring state, respectively. The X-ray spectra of the source can be well-described with single power-law models in both exposures. The derived X-ray photon index and the flux density at 1 keV were found to be Gamma = 1.65 +/- 0.02 and S(1) (keV) = 215 +/- 5 nJy in the quiescent state. In the flaring state, the source exhibited a harder X-ray spectrum (Gamma = 1.50 +/- 0.01) with a nearly doubled X-ray flux density of S(1 keV) = 404(-5)(+6) nJy Moreover, significant hard X-ray signals were detected up to similar to 27 keV. In cooperation with Suzaku, simultaneous radio, optical, and very-high-energy gamma-ray observations of OJ 287 were performed with the Nobeyama Millimeter Array, the KANATA telescope, and the MAGIC telescope, respectively. The radio and optical fluxes in the flaring state (3.04 +/- 0.46 Jy and 8.93 +/- 0.05 mJy at 86.75 Hz and in the V-band, respectively) were found to be higher by a factor of 2-3 than those in the quiescent state (1.73 +/- 0.26 Jy and 3.03 +/- 0.01 mJy at 86.75 Hz and in the V-band, respectively). No notable gamma-ray
MISC
364講演・口頭発表等
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The Astrophysical Journal Letters 2009年
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Publications of the Astronomical Society of Japan 2009年
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The Astrophysical Journal 2009年
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Publications of the Astronomical Society of Japan 2009年
共同研究・競争的資金等の研究課題
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