研究者業績
基本情報
- 所属
- 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 宇宙物理学研究系 教授総合研究大学院大学 先端学術院 宇宙科学コース 教授東京工業大学 理学院物理学系物理学コース 特定教授関西学院大学 大学院理工学研究科 客員教授
- 学位
- 理学博士(東京大学)
- J-GLOBAL ID
- 200901025041369206
- researchmap会員ID
- 1000144439
専門はＸ線天文学。特に、中性子星やブラックホールを含むX線連星の観測的研究および衛星搭載X線CCDカメラの開発研究。
受賞
1-
1996年
論文
201-
Publications of the Astronomical Society of Japan 60(SPEC. ISS. 1) 2008年 査読有り
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Progress of theoretical physics. Supplement 169 316-321 2007年12月19日Orbital calibrations of the XIS, in terms of the energy scale, energy resolution, and quantum efficiency, are needed not only to confirm the calibrations on the ground but also to examine inevitable performance change in orbit. Fundamentals of the XIS calibration issues have been established and are implemented the softwares and the data base for general observers. We overview the current status of the XIS calibration in orbit.
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6TH INTEGRAL WORKSHOP: THE OBSCURED UNIVERSE 622 521-+ 2007年 査読有りAs system similar to a rotating neutron star, a strongly magnetized white dwarf (WD) may be a moderate particle acceleration site. At the best case, the induced electric field is expected to reach 10(13) to 10(14) eV. A trial to detect non-thermal emission from a best candidate among WDs, AE Aquarii, was performed with the hard X-ray detector (HXD) on-board the fifth Japaneses X-ray satellite, Suzaku. Although the HXD has a non-imaging capability, the sensitivity in the 10 - 70 keV band reaches about the 5 x 10(-6) - 10(-5) photons/sec/cm(2)/keV level with only 100 ksec exposure. Marginal detection has been achieved with the HXD, which was separated from the thermal emission. If this is real, it must be the first case of a detection of non-thermal emission from ArDs.
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2007 IEEE NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, VOLS 1-11 2526-+ 2007年 査読有りWe report in-flight status of the X-ray detectors on board the Suzaku observatory, the 5th X-ray astronomy satellite of Japan launched on July 10, 2005. Suzaku is equipped with two types of instruments: one is the X-ray Imaging Spectrometers (XISs) and the other is Hard X-ray Detector (HXD). XIS utilizes the X-ray CCD camera in combination with the grazing-incidence X-ray telescope. HXD is a non-imaging, hybrid detector utilizing Si PIN diodes and GSO/BGO phoswich counters. Suzaku takes a low-earth, circular orbit with an altitude of 560 km and an inclination of 31 deg. This means that Suzaku goes through the south atlantic anomaly about 1/3 of its revolutions. This has a large impact on the in-flight performance of XIS and HXD, which is reported in detail in the present paper.
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Progress of theoretical physics. Supplement (169) 225-228 2007年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 2-50keV 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 1.4keV to 1.2keV 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 Ka at 7.0keV and 6.7keV. The energies of these absorption lines suggest a blue shift with an outflow velocity of～1000km s^<-1>. The H-like iron Kα equivalent width remains approximately constant at～30eV over all the observations, while that of the He-like Kα line increases from 7eV to 20eV. 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 200-2000km s^<-1>, and the size of the plasma as～10^<10> cm assuming a source distance of 10kpc.
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UV, X-RAY, AND GAMMA-RAY SPACE INSTRUMENTATION FOR ASTRONOMY XV 6686 2007年 査読有りThe CCD detectors in the X-ray Imaging Spectrometers (XIS) aboard Suzaku have been equipped with a precision charge injection capability. The purposes of this capability are to measure and reduce the detector degradation caused by charged particle radiation encountered on-orbit. Here we report the first results from routine operation of the XIS charge injection function. After 12 months' exposure of the XIS to the on-orbit charged particle environment, charge injection already provided measurable improvements in detector performance: the observed width of the 5.9 keV line from the onboard calibration source was reduced from 205 eV to less than 145 eV. The rate of degradation is also significantly smaller with charge injection, so its benefit will increase as the mission progresses. Measured at 5.9 keV, the radiation-induced rate of gain degradation is reduced by a factor of 4.3 +/- 0.1 in the front-illuminated sensors when injecting charge greater than 6 keV equivalent per pixel. The corresponding rate of degradation in spectral resolution is reduced by a factor 6.5 +/- 0.3. Injection of a smaller quantity of injected charge in the back-illuminated XIS sensor produces commensurately smaller improvement factors. Excellent uniformity of the injected charge pattern is essential to the effectiveness of charge injection in the XIS.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 208-213 2007年 査読有りWe summarize the presentations in this session from a point of view of particle acceleration in the vicinity of a magnetized neutron star and a white dwarf. We take the radio and hard X-ray emission as a clue for the particle acceleration, and summarize the results of the past observations in the literature. Efficient particle acceleration seems to be working only in the isolated, highly magnetized neutron stars. In the mass-accreting, highly magnetized objects, particle acceleration and even the production of hot, thin thermal plasma seem to be suppressed.
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PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (169) 316-321 2007年 査読有りOrbital calibrations of the XIS, in terms of the energy scale, energy resolution, and quantum efficiency, are needed not only to confirm the calibrations on the ground but also to examine inevitable performance change in orbit. Fundamentals of the XIS calibration issues have been established and are implemented the softwares and the data base for general observers. We overview the current status of the XIS calibration in orbit.
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UV, X-RAY, AND GAMMA-RAY SPACE INSTRUMENTATION FOR ASTRONOMY XV 6686 id.66860P 2007年The energy resolution of the X-ray CCDs onboard the Suzaku satellite (X-ray Imaging Spectrometer: XIS) has been degraded since the launch due to radiation damage. To recover from this, we have applied a spaced-row charge injection (SCI) technique to the Suzaku XIS in orbit. By injecting charge into CCD rows periodically; the energy resolution 14 months after launch is improved from 210 eV to 150 eV at 5.9 keV, which is close to the resolution just after the launch (140 eV). Additional information on these results is given in a companion paper by the XIS team. In this paper, we report the details of CCD charge transfer inefficiency (CTI) in the SCI mode, the correction method, and the implementation of it in ground analysis software for XIS data. In the SCI mode; CTI depends on the distance of a charge packet from the nearest charge-injected row, and the gain shows a periodic non-uniformity. Using flight data obtained with the onboard calibration sources; as well as a cosmic source (the Perseus cluster of galaxies), we studied the non-uniformity in detail. We developed a method to correct for the non-uniformity that will be valuable as the radiation damage progresses in future.
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Advances in Space Research 40(10) 1485-1490 2007年 査読有り
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IEEE Nuclear Science Symposium Conference Record 4 2526-2531 2007年 査読有り
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Proceedings of the SICE Annual Conference 3019-3024 2007年 査読有り
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Proceedings of the International Astronomical Union 2(238) 23-28 2006年8月 査読有り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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 58(3) 587-594 2006年6月 査読有りWe analyzed an effect of the photo-ionization on the continuum spectra using the XMM-Newton archive data of the low-mass X-ray binary EXO 0748-676. We found that the ionization degree of the circumstellar plasma, which modifies the soft X-ray spectrum through absorption, changes largely in association with the X-ray bursts and the dips. The burst light curve below similar to 1 keV is found to have a major contribution from the persistent emission, which temporary increased during the burst due to a reduction of the opacity of the absorber. We utilized a correlation diagram of the count rates (0.5-1.0 keV vs. 2.0-4.0 keV) to study the effect of photo-ionization during the dips. We found that the correlation can be much better reproduced if we take into account the photo-ionization of the absorber. No partial covering absorption was required, except for the residual flux in the deepest dips.
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European Space Agency, (Special Publication) ESA SP 2(604) 975-976 2006年 査読有りWe give overview and the current status of the development of the Soft X-ray Imager (SXI) onboard the NeXT satellite. SXI is a back-illuminated supportless CCD (a combination of "back-illuminated CCD" and "supportless CCD") whose imaging area and the supportless region are 42 × 42mm2 and 30mmφ respectively. The goal of the thickness of the depletion layer is 300μm, which enables us to cover the energy range of 0.3 - 25 keV. The evaluation model 'CCD-NeXT1' with the size of 24 × 48mm2 shows no performance change due to the thinning process. The test model of P-channel CCD was confirmed to have high quantum efficiency above 10 keV with an equivalent depletion layer of 300m.
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European Space Agency, (Special Publication) ESA SP 622(622 SP) 325-332 2006年 査読有り
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Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray, Pts 1 and 2 6266 Y2662-Y2662 2006年 査読有りWe report on the origin of the instrumental background of the X-ray CCD camera in space obtained from the Monte Carlo simulation with GEANT4. In the space environment, CCD detects many non-X-ray events, which are produced by the interactions of high-energy particles with the materials surrounding CCD. Most of these events are rejected through the analysis of the charge split pattern, but some are remained to be background. Such instrumental background need to be reduced to achieve higher sensitivity especially above several keV. We simulated the interactions of the cosmic-rays with the CCD housing, and extracted the background events which escaped from the screening process by the charge split pattern. We could reproduce the observed spectral shape of the instrumental background of Suzaku XIS on orbit with the Monte Carlo simulation. This means that the simulation succeeded to duplicate the background production process in space. From the simulation, we found that the major components of the background in the front-side illuminated CCD are the recoil electrons produced by the Compton-scattering of the hard X-ray photons in the CCD. On the other hand, for the backside illuminated CCD, contribution from the low energy electrons becomes dominant, which are produced by the interactions of cosmic-ray protons or hard X-rays with the housing. These results may be important to design the X-ray CCD camera for the future missions, such as NeXT.
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Space Telescopes and Instrumentation II: Ultraviolet to Gamma Ray, Pts 1 and 2 6266 26641-26641 2006年 査読有りThe X-ray Imaging Spectrometer on the Suzaku satellite consists three front-illuminated (FI) and one backilluminated (BI) CCD cameras. Using ground calibration data taken at Kyoto University and Osaka University, we obtained the energy response of the XIS, which consists of at least six components: 1. a main peak, 2. a sub peak, 3. a triangle component, 4. a Si escape, 5. a Si line, and 6. a constant component. The relation between the energy and the pulse height was also estimated, which is called as a gain. The relation cannot be represented with a single linear function. Then we divided the gain into two parts at the Si edge (1.839 keV) and each part can be described with a single linear function. Thus there is a discontinuity at 1.839 keV in the XIS gain. We have monitored the variation of the gain and energy resolution in orbit by observing the calibration source of Fe-55 illuminating two corners of each CCD.
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SPACE TELESCOPES AND INSTRUMENTATION II: ULTRAVIOLET TO GAMMA RAY, PTS 1 AND 2 6266 id. 62662I 2006年We give overview and the current status of the development of the Soft X-ray Imager (SXI) onboard the NeXT satellite. SXI is an X-ray CCD camera placed at the focal plane detector of the Soft X-ray Telescopes for Imaging (SXT-I) onboard NeXT. The pixel size and the format of the CCD is 24 x 24 mu m (IA) and 2048 x 2048 x 2 (IA+FS). Currently, we have been developing two types of CCD as candidates for SXI, in parallel. The one is front illumination type CCD with moderate thickness of the depletion layer (70 similar to 100 mu m) as a baseline plan. The other one is the goal plan, in which we develop back illumination type CCD with a thick depletion layer (200 similar to 300 mu m). For the baseline plan, we successfully developed the proto model 'CCD-NeXT1' with the pixel size of 12 mu m x 12 mu m and the CCD size of 24mm. x 48mm. The depletion layer of the CCD has reached 75 similar to 85 mu m. The goal plan is realized by introduction of a new type of CCD T-channel CCD', which collects holes in stead of electrons in the common 'N-channel CCD'. By processing a test model of P-channel CCD we have confirmed high quantum efficiency above 10 keV with an equivalent depletion layer of 300 mu m. A back illumination type of P-channel CCD with a depletion layer of 200 mu m with aluminum coating for optical blocking has been also successfully developed. We have been also developing a thermo-electric cooler (TEC) with the function of the mechanically support of the CCD wafer without standoff insulators, for the purpose of the reduction of thermal input to the CCD through the standoff insulators. We have been considering the sensor housing and the onboard electronics for the CCD clocking, readout and digital processing of the frame date.
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Astrophysical Journal 648(2 II) 2006年 査読有り
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 541(1-2) 357-364 2005年4月 査読有りAstro-E2 is the fifth Japanese X-ray astronomical satellite and will be launched in 2005. The Astro-E2 X-ray Imaging Spectrometers (XISs) consist of four sets of X-ray CCD cameras. Each CCD camera has an imaging area of 1024 x 1024 pixels and covers a region of 18' x 18' on the sky combined with an X-ray Telescope. One XIS will utilize backside illuminated (BI) CCDs, and the other three will be equipped with front-side illuminated (171) CCDs. The BI CCD has a higher quantum efficiency than the FI CCD below 2 keV, while the FI CCD is more sensitive to X-rays above 5 keV than the BI CCD. Both types of the CCDs have nearly the same energy resolution (full-width at half-maximum (FWHM) =similar to 130 eV at 6 keV). All four cameras have a charge injection capability and Fe-55 calibration sources, and we can correct the change of the gain and recover the degradation of the energy resolution due to radiation damage caused by cosmic rays. The sensors are cooled to -90 degrees C to minimize thermal noise in orbit. The low temperature is also helpful to reduce the influence of the radiation damage. (c) 2005 Elsevier B.V. All rights reserved.
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NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 541(1-2) 392-397 2005年4月 査読有りWe give an overview, the current status and future plan of the development of the Soft X-ray Imager (SXI) onboard the NeXT (Non-thermal Energy eXploration Telescope) satellite proposed to be launched around 2010. The SXI is a back-illuminated supportless CCD (a combination of "back-illuminated CCD" and "supportless CCD") whose imaging area size and the supportless region are 42 mm x 42 mm and 30 mm phi, respectively. The goal of the depletion layer of the CCD is 300 mu m, which enable us to cover the X-ray energy range of 0.5-20 keV. The first test model of the supportless CCD shows no performance change due to the thinning process of the CCD. We have already started processing the evaluation model 'CCD-NeXT1', which will be completed at the end of 2004. We are also studying the camera system, the focal plane assembly including thermal electric cooler (TEC) and electronics as well as the CCD chip. (c) 2005 Published by Elsevier B.V.
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ASTROPHYSICAL JOURNAL 609(1) 325-334 2004年7月 査読有りWe present the results of high-resolution spectroscopy of absorption-line features of highly ionized ions in the X-ray spectra of GX 13+1 with the Chandra HETGS. We have resolved Kalpha absorption lines of hydrogen-like Fe, Mn, Cr, Ca, Ar, S, Si, and Mg ions and helium-like Fe ions. Applying the Voigt profile to these spectral features, we find that the plasma responsible for the absorption lines has a significant blueshift of 460 +/- 70 km s(-1), indicating an outflow velocity of approximate to 400 km s(-1) corrected for the proper motion, with a line-of-sight velocity dispersion of 490(-140)(+110) km s(-1). The plasma is photoionized with an ionization parameter of log xi similar or equal to 4.1-4.7. The inferred mass outflow rate is 0.7 x 10(18) g s(-1) or higher, comparable to the mass accretion rate ( 10(18) g s(-1)) estimated from the continuum spectrum. This indicates that the mass outflow plays a significant role to determine the whole dynamics of the accretion disk. We consider a simplified radiation-driven disk wind model for the origin of the outflow. Our observations are explained by the wind originating from radii of similar to 10(10) - 10(11) cm with a density greater than or similar to10(13) cm(-3).
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ASTROPHYSICAL JOURNAL 554(1) 316-321 2001年6月 査読有りWe have detected pulsed X-ray emission from the fastest millisecond pulsar known, PSR B1937+21 (P = 1.558 ms), with ASCA. The pulsar is detected as a point source above similar to 1.7 keV, with no indication of nebulosity. The source flux in the 2-10 keV band is found to be f= (3.7 +/- 0.6) x 10(-13) ergs s(-1) cm(-2) which implies an isotropic luminosity of L-X = 4 piD(2)f similar to (5.7 +/- 1.0) x 10(32)(D3.6 kpc)(2) ergs s(-1), cm where D is the distance, and an X-ray efficiency of similar to5 x 10(-4) relative to the spin-down power of the pulsar. The pulsation is found at the period predicted by th radio ephemeris with a very narrow primary peak, the width of which is about 1/16 phase (similar to mus), near the time resolution limit (61 mus) of the observation. The instantaneous flux in the primary peak (1/16 phase interval) is found to be (4.0 +/- 0.8) x 10(-12) ergs s(-1) cm(-2). Although there is an indication for the secondary peak, we consider its statistical significance too low to claim a definite detection. The narrow pulse profile and the detection in the 2-10 keV band imply that the X-ray emission is caused by the magnetospheric particle acceleration. Comparison of X-ray and radio arrival times of pulses indicates, within the timing errors, that the X-ray pulse is coincident with the radio interpulse.
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ASTROPHYSICAL JOURNAL 550(2) 1007-1022 2001年4月 査読有りWe report observation results of the supersoft X-ray sources CAL 87 and RX J0925.7-4758 with the X-ray CCD cameras (Solid-State Imaging Spectrometers [SISs]) on board ASCA. Because of the superior energy resolution of the SIS (DeltaE/E similar to 10% at 1 keV) relative to previous instruments, we could study detailed X-ray spectral structures of these sources for the first time. We have applied theoretical spectral models to CAL 87 and constrained the white dwarf mass and intrinsic luminosity as 0.8-1.2 M. and 4 x 10(37)-1.2 x 10(38) ergs s(-1), respectively. However, we have found the observed luminosity is an order of magnitude smaller than the theoretical estimate, which indicates that the white dwarf is permanently blocked by the accretion disk, and we are observing a scattering emission by a fully ionized accretion disk corona (ADC) whose column density is similar to1.5 x 10(23) cm(-2). Through simulation we have shown that the orbital eclipse can be explained by the ADC model, such that a part of the extended X-ray emission from the ADC is blocked by the companion star filling its Roche lobe. We have found that very high surface gravity and temperature, similar to 10(10) cm s(-2) and similar to 100 eV, respectively, as well as a strong absorption edge at similar to1.02 keV, are required to explain the X-ray energy spectrum of RX J0925.7-4758. These values are only possible for an extremely heavy white dwarf near the Chandrasekhar limit. Although the supersoft source luminosity should be similar to 10(38) ergs s(-1) at the Chandrasekhar limit, the observed luminosity of RX J0925.7-4758 is nearly 2 orders of magnitude smaller, even assuming an extreme distance of similar to 10 kpc. To explain the luminosity discrepancy, we propose a model in which very thick matter that was previously ejected from the system, as a form of jets, intervenes the line of sight and reduces the luminosity significantly because of Thomson scattering.
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 321(4) 776-782 2001年3月 査読有りWe have searched the rising portion of type I X-ray bursts observed from the Rapid Burster with the Rossi X-ray Timing Explorer for the presence of periodicities. The 95 per cent confidence upper limit on the average rms variation of near coherent pulsations with a width of less than or similar to1 Hz (in 60-2048 Hz) during the first second of the bursts is <8.8 per cent. We find a possible detection (> 98 per cent significance) at 306.5 Hz.
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NEW CENTURY OF X-RAY ASTRONOMY 251 514-515 2001年 査読有りWe report on the development of the ISAS Ginga archive. At ISAS, all the Ginga archive and analysis software were originally developed on the main-frame computers. We are installing them to the UNIX environment with minor modification so that all the analysis will become possible in the modern network computing environment. The archive will be made public from ISAS PLAIN Center (Center for Planning and information systems) in near future.
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NEW CENTURY OF X-RAY ASTRONOMY 251 382-383 2001年 査読有りAbsorption lines at similar to4.1 keV have been detected in the type I burst spectra of three sources, including X1608-52. If these lines are interpreted as redshifted resonance line of He-like iron ions, a large gravitational redshift (1 + z similar to 1.7) is required. This imposes a constraint on the neutron star structure. We have observed X1608-52 with ASCA for similar to 10 d in Feb. 2000. We report our systematic search for these lines in the 11 burst spectra obtained with the SIS in FAST mode. Our nondetection of any clear line feature from either one of the 11 bursts leads us to conclude that the absorption line, if it has an equivalent width like that detected by Tenma (120 eV), is intrinsically broad (W-eq greater than or equal to 100 eV), or none of the 11 bursts exhibit the significant absorption features.
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FROM DARKNESS TO LIGHT: ORIGIN AND EVOLUTION OF YOUNG STELLAR CLUSTERS 243 561-570 2001年 査読有りTo investigate X-ray emission from protostars and T Tauri stars, we observed two star forming regions, L1630 in Orion and IC348 in Perceus with the X-ray observatory ASCA. From the observation of L1630, we detected X-ray emission from the region where two Class I protostars SSV63E and SSV63W are located (hereafter SSV63E+W). The spectrum of SSV63E+W is well explained by an optically thin thermal plasma model with a high temperature of kT = 5.0 (3.3-7.9) keV and a heavy at sorption of N-H = 1.5 (1.2-1.8) x 10(23) cm(-2), suggesting that it is enbedded deep in the: surrounding dusts. A significantly large X-ray flare was detected from SSV63E+W during the present ASCA observation with the heal: flux of about 9 times that of the quiescent flux. The 0.5-10 keV luminosity of SSV63E+W was about 1 x 10(32) erg s(-1) in the quiescent state. We detected 20 X-ray sources from IC348, 17 of which were identified with the ROSAT X-ray sources. We detected two X-ray flares from the center region of IC348. One of the flare exhibited an intersting feature that the hard X-ray flare in 2.0-7.0 keV band rose faster than the soft X-ray flare in 0.7-2.0 keV band. Combining the Hare light curves with the spectral evolution of the flare, we concluded that the temperature reached to the peak earlier than the emission measure along the progress of the flare. This time lag between the temperature peal: and the peak of emission measure was observed for the first time from T Tauri stars, while such time lags are often observed in solar flares.
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ASTROPHYSICAL JOURNAL 537(1) 319-326 2000年7月 査読有りWe present new observations of two anomalous X-ray pulsars (AXPs), 4U 0142+61 and 1E 1048.1-5937, made in 1998 with ASCA. The energy spectrum of each of these two AXPs is found to consist of two components, a power-law and a blackbody emission from the neutron star surface. These observations, when compared with earlier ASCA observations in 1994, show remarkable stability in the intensities, spectral shapes, and pulse profiles. However, we find that the spin-down rate in 1E 1048.1-5937 is not constant. In this source, we have clearly identified three epochs with spin-down rates different from each other and from the average value. This has very strong implications for the magnetar hypothesis for AXPs. We also note that the spin-down rate and its variations in 1E 1048.1-5937 are much larger than can normally be produced by an accretion disk with a very low mass accretion rate corresponding to its low X-ray luminosity.
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X-RAY OPTICS, INSTRUMENTS, AND MISSIONS III 4012 123-136 2000年 査読有りSoft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4-2.2 keV range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is-fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Neverthless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.
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Advances in Space Research 25(3-4) 449-452 2000年 査読有りWe report on the result of the X-ray observation of X-ray Nova Velorum 1993 (GRS 1009-45), made with ASCA on November 10-11, 1993. The energy spectrum was extremely soft and accompanied by a hard tail, characteristics of the Galactic black-hole binaries in the soft state. It is well represented by a two component model consisting of a multicolor disk model or a general relativistic accretion disk model, both describing emission from an optically-thick accretion disk, and a power-law component with a photon index of ∼ 2.5. Spectral analysis of the soft component allows estimation of the mass of the central object. For the optically-estimated distance (> 1 kpc) and inclination (> 37°), the mass is estimated to be > 3.1 M⊙. These results strongly support that the compact object is a black hole. © 2000 COSPAR. Published by Elsevier Science Ltd.
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PULSAR ASTRONOMY - 2000 AND BEYOND: IAU COLLOQUIUM 177 202 353-354 2000年 査読有りWe report the first detection of the pulsed X-ray emission from the fastest millisecond pulsar known PSR B1937+21 (P =1.558msec) with ASCA. The pulsar is detected as a point source above similar to 1.7keV, with no nebulosity indicated. The source flux in the energy band 2-10keV is found to be f = 4.3 x 10(-13)erg s(-1) cm(-2), which corresponds to the luminosity of L-x = 4 pi D(2)f approximate to 6.6 x 10(32)(D/3.6kpc)(2) erg s(-1), where D is the distance, and correspond to approximate to 6 x 10(-4) of the rotation power of the pulsar. The pulsation is found at the period predicted by the radio ephemerides with very narrow primary peaks, the width of which is about 1/16 phase approximate to 100 mu s near the time resolution limit (61 mu s) of the observation. The pulsed luminosity within the primary peak (1/16 phase interval) is found to be f(p) = 4.0 x 10(-12)erg s(-1) cm(-2) Although there may be a secondary peak, its statistical significance is too low to identify. Spectra of the whole source region and the primary peak are fitted by power law models to give photon indices of about unity for both.
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Proceedings of SPIE - The International Society for Optical Engineering 4012 123-136 2000年Soft X-ray response of X-ray Imaging Spectrometers (XIS) for the Astro-E satellite is measured with a grating spectrometer system at Osaka. First, relation between incident X-ray energy and output pulse height peak (E-PH relation) is examined with an SX grating. It is found that jump in the E-PH relation around Si-K edge is at most 2.7 eV. Second, quantum efficiency (QE) of the XIS in 0.4-2.2 kev range is measured relatively to the reference CCD of which absolute QE was calibrated with a gas proportional counter. The QE is fitted with a model in which CCD gate structures are considered. Systematic error on the QE results is estimated by referring an independent measurement. Third, tuning and improvement of the response function is performed. We employ six components to reproduce the response profile of the XIS. In this paper, improvement of one component which is originated in the events absorbed in the channel-stop is presented. Neverthless, Astro-E was lost due to the launch failure. We overview the XIS project in its flight model phase, modified points of the design, problems and solutions etc., in order to be utilized in a possible recovery of the satellite.
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ASTROPHYSICAL JOURNAL 523(1) L69-L72 1999年9月20日 査読有り
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Astronomische Nachrichten 320(4-5) 353 1999年 査読有り
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Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 436(1-2) 79-84 1999年 査読有り
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ASTRONOMISCHE NACHRICHTEN 320(4-5) 348-348 1999年 査読有り
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ASTRONOMISCHE NACHRICHTEN 320(4-5) 215-216 1999年 査読有りX-ray properties of the Galactic jet sources are studied using the ASCA data. Two different types are found in the jet sources. One type, represented by the superluminal jet sources GRO J1655-40 and GRS1915+105, includes a rapidly rotating compact star (a black hole or a neutron star) receiving super-critical mass accretion. On the other hand, relatively dim sources, such as GX339-4, 1E1740.7-2942 and GRS 1758-258, may constitute of the other type, which can produce jets at luminosities much lower than the Eddington limit.
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ASTRONOMISCHE NACHRICHTEN 320(4-5) 340-340 1999年 査読有り
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ASTRONOMISCHE NACHRICHTEN 320(4-5) 343 1999年 査読有り
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ASTROPHYSICAL JOURNAL 508(2) L167-L170 1998年12月 査読有りWe observed the newly discovered Galactic jet source XTE J0421 + 560 (=CI Camelopardalis) with ASCA from 1998 April 3.3 to April 4.1 (UT), 3 days after the beginning of the outburst. The X-ray intensity in the 1-10 keV band gradually decreased with an e-folding time of about 30 hr; the decline was accompanied by spectral softening. Two flarelike intensity enhancements were detected below similar to 1 keV. We could fit the average spectrum above 0.8 keV with a two-temperature model (5.7 and 1.1 keV) of thermal emission from an optically thin ionization-equilibrium plasma. The broad iron K profile, however, requires an extra emission line at 6.4 keV or Doppler broadening (or both). The former can be explained in terms of reflection from cold matter, while the latter can be attributed to emission from the twin jets. In both cases, the time evolution of the emission measure and of the temperature are difficult to explain by emission from a single plasma, suggesting that heat input and/or injection of material was occurring during the outburst.
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ASTROPHYSICAL JOURNAL 503(2) L143-L146 1998年8月 査読有りWe have investigated the energy spectrum and the orbital modulation of the supersoft X-ray source CAL 87 using the ASCA satellite. We have detected a deep absorption edge at 0.85(-0.01)(+0.02) keV superposed on a continuum that can be approximated with an absorbed blackbody (kT = 0.05(-0.01)(+0.06) keV). The edge structure may be produced by the highly ionized species of O VIII and O VII. Such deep edge structures from highly ionized heavy elements are expected for X-ray emission from a white dwarf with an envelope of stable hydrogen burning and strongly supports the model that a white dwarf with a large mass accretion rate is involved in the supersoft X-ray sources. Epoch-folding analysis reveals the presence of a partial X-ray eclipse with broad wings at orbital phase 0; the eclipse covers a quarter of the orbital phase and the X-ray flux decreases down to similar to 40% of the out-of-eclipse level. We discuss the possible cause of the partial eclipse, including the extended emission region due to the accretion disk corona, and the X-ray scattering site formed by the gas escaping from the binary system, where the gas is highly ionized by the large X-ray luminosity from the white dwarf.
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ASTROPHYSICAL JOURNAL 495(1) 435-439 1998年3月A new X-ray pulsar, AX J1820.5-1434, has been discovered during the ASCA Galactic plane survey project on April 9, at R.A. = 18(h)20(m)29.(s)5, decl. = -14 degrees 34'24 " (equinox 2000.0; error radius 0.'5). A coherent pulsation was detected from the source with an apparent barycentric pulse period of 152.26 +/- 0.04 s. The mean flux, not corrected for the interstellar absorption, was 2.3 x 10(-11) ergs s(-1) cm(-2) in the 2-10 keV energy band. The energy spectra obtained by the GIS and SIS can be fitted by a power-law model (photon index = 0.9 +/- 0.2) with a large column density of 9.8 +/- 1.7 x 10(22) H atoms cm(-2). These parameters indicate that the new pulsar is a highly obscured accretion-driven binary X-ray pulsar. This discovery of a faint pulsar suggests existence of many hidden pulsars in our Galaxy.
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ASTROPHYSICAL JOURNAL 493(2) L75-L78 1998年2月 査読有りWe report results from simultaneous ASCA and RXTE observations of Cygnus X-1 when the source made a rare transition from the hard (=low) state to the soft (=high) state in 1996. These observations together cover a broad energy range similar to 0.7-50 keV with a moderate energy resolution at the iron K band and thus make it possible to disentangle various spectral components. The low-energy spectrum is dominated by an ultrasoft component, which is likely to be the emission from the hottest inner portion of the accretion disk around the black hole. At high energies, the X-ray spectrum can be described by a Comptonized spectrum with a reflection component. The Compton corona, which upscatters soft "seed photons" to produce the hard X-ray emission, is found to have a y-parameter similar to 0.28. The hard X-ray emission illuminates the accretion disk, and the reemitted photons produce the observed "reflection bump." We show that the reflecting medium subtends only a small solid angle (similar to 0.15 x 2 pi but has a large ionization parameter such that iron is ionized up to Fe XXIV-Fe XXVI. The presence of a broad iran line at 6.58 +/- 0.04 keV is also consistent with a highly ionized disk, if we take into account the gravitational and Doppler shift of the line energy. These results imply a geometry of a central corona surrounding the black hole and the reflection occurring in the innermost region of the disk where matter is highly ionized.
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ASTROPHYSICAL JOURNAL 494(2) L207-L210 1998年2月 査読有りWe report a rare discovery of a fast (69 ms) pulsar using X-ray data acquired with the Advanced Satellite for Cosmology and Astrophysics (ASCA). The highly significant detection arises from the serendipitous ASCA X-ray source AXS J161730-505505, located near the young Galactic supernova remnant (SNR) RCW 103. The epoch-folded light curve displays a single asymmetric pulse profile with a pulse fraction of similar to 50%. Spectral fits to the high-energy (i.e., greater than 3.5 keV) source data using a simple absorbed power-law model, assuming the hydrogen column density to the SNR, gives a photon index gamma = 1.6(-0.3)(+0.2) and an unabsorbed flux of similar to 6.4 x 10(-12) ergs cm(-2) s(-1). The extracted source spectrum below 3.5 keV is contaminated by mirror-scattered soft thermal emission from the similar to 9' diameter RCW 103, whose projected center is located just similar to 7' away. If the pulsar is associated with the remnant, the implied neutron star velocity is at the high end of the pulsar velocity distribution for the distance estimates to the remnant but still plausible. We suggest that AXS J161730-505505 is likely a young rotation-powered pulsar with a characteristic spin-down age of similar to 8000 yr. The physical association of the pulsar with RCW 103 and its central source, 1E 161348-5055, remains intriguing.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 50(1) 25-30 1998年2月 査読有りX-ray observations of the nearby starburst galaxy IC 342 with ASCA led to the detection of three bright X-ray sources, whose positions are consistent with those from the Einstein and ROSAT observations. The X-ray luminosities of the two sources exceed the Eddington limit of a 1.4M. object by two orders of magnitude for an assumed distance of 4.5 Mpc. The brightest one (source I) among the three exhibited significant time variations on a time scale of a few hours during the ASCA observation. Thus, the size of the emission region must be smaller than about 10(14) Cm. The energy spectrum of the source can be represented either by a power-law with an exponential roll-over, or by an optically thick accretion disk model with a maximum color temperature of 1.77 keV. Although the large luminosity of source 1 may be explained by a similar to 100 M. black hole at 4.5 Mpc, the observed energy spectrum is too hard to be accounted for by an optically thick accretion disk around the black hole. If source 1 is a relativistic jet source with strong X-ray beaming, both the large luminosity and the hard X-ray spectrum can be explained.
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ASTROPHYSICAL JOURNAL 492(2) 761-766 1998年1月 査読有りWe analyze X-ray archive data of the W UMa-type binary VW Cephei taken with ASCA on 1993 November 5-6. By analyzing the light curve, we find a long-duration flare of approximate to 7.5 hr with a peak luminosity of 1.2 x 10(30) ergs s(-1) (0.4-3.0 keV) for the assumed distance of 23.2 pc. A flux dip is detected in the light curve at the orbital phase of similar to 0.5, and it is identified as an eclipse by the secondary star. We determine the timescale of the eclipse egress to be similar to 30 minutes from a model fit to the light curve. With this timescale, we estimate that the linear size of the flaring region is approximate to 5.5 x 10(10) cm, regardless of the flare models. From the spectral analysis of the data, we find that the spectrum can be well reproduced by the variable-abundance plasma model with a combination of two different temperatures, kT = 0.64 and kT = 1.91 keV. The hotter component is considered to be associated with the flare. The results are interpreted in terms of a two-ribbon flare model, in which we also discuss the possible enhancement of element abundances.
MISC
200所属学協会
4-
2000年1月 - 現在
共同研究・競争的資金等の研究課題
15-
日本学術振興会 科学研究費助成事業 基盤研究(C) 2019年4月 - 2023年3月
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日本学術振興会 科学研究費助成事業 新学術領域研究(研究領域提案型) 2012年6月 - 2017年3月
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日本学術振興会 科学研究費助成事業 2012年4月 - 2015年3月
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日本学術振興会 科学研究費助成事業 基盤研究(B) 2010年4月 - 2013年3月
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日本学術振興会 科学研究費助成事業 特別研究員奨励費 2005年 - 2007年
● 指導学生等の数
1-
年度2021年度(FY2021)修士課程学生数2連携大学院制度による学生数2学術特別研究員数1
● 専任大学名
1-
専任大学名総合研究大学院大学（SOKENDAI)
