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 特任准教授
- 学位
- 博士(東京大学)
- J-GLOBAL ID
- 200901062224980497
- researchmap会員ID
- 1000368169
- 外部リンク
研究キーワード
10経歴
7-
2007年10月 - 現在
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2003年10月 - 2007年9月
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2003年10月 - 2007年9月
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2003年3月 - 2003年9月
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2003年3月 - 2003年9月
学歴
4委員歴
2-
2017年6月 - 2019年6月
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2013年4月 - 2019年4月
論文
295-
Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 52-52 2024年8月21日
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 236-236 2024年8月21日
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 224-224 2024年8月21日
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 235-235 2024年8月21日
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 61-61 2024年8月21日
MISC
243-
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(6) 1217-1228 2009年12月Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were carried out. K-shell transition lines from highly ionized ions of various elements were detected, including Chromium (Cr-K alpha at 5.61 keV). The X-ray continuum spectra were modeled in the 3.4-40keV band, summed over the entire remnant, and were fitted with a simplest combination of the thermal bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits with this assumption indicate that the continuum emission is likely to be dominated by non-thermal emission with a cut-off energy at > 1 keV. The thermal-to-non thermal fraction of the continuum flux in the 4-10 keV band is best estimated as similar to 0.1. Non-thermal-dominated continuum images in the 4-14 keV band were made. The peak of the non-thermal X-rays appears at the western part. The peak position of the TeV gamma-rays measured with HEGRA and MAGIC is also shifted at the western part with the I-sigma confidence. Since the location of the X-ray continuum emission was known to be presumably identified with the reverse shock region, the possible keV-TeV correlations give a hint that the accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements in the reverse shock region.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(6) 1217-1228 2009年12月Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were carried out. K-shell transition lines from highly ionized ions of various elements were detected, including Chromium (Cr-K alpha at 5.61 keV). The X-ray continuum spectra were modeled in the 3.4-40keV band, summed over the entire remnant, and were fitted with a simplest combination of the thermal bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits with this assumption indicate that the continuum emission is likely to be dominated by non-thermal emission with a cut-off energy at > 1 keV. The thermal-to-non thermal fraction of the continuum flux in the 4-10 keV band is best estimated as similar to 0.1. Non-thermal-dominated continuum images in the 4-14 keV band were made. The peak of the non-thermal X-rays appears at the western part. The peak position of the TeV gamma-rays measured with HEGRA and MAGIC is also shifted at the western part with the I-sigma confidence. Since the location of the X-ray continuum emission was known to be presumably identified with the reverse shock region, the possible keV-TeV correlations give a hint that the accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements in the reverse shock region.
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ASTRONOMY & ASTROPHYSICS 501(3) 1047-1058 2009年7月Context. A significant number of cataclysmic variables have been detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type. Aims. We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class. Methods. Timing and spectral analysis of IGR J00234+6141 are based on an XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725, we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data. Results. We determine a spin period of 561.64 +/- 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to similar to 2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 +/- 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of similar to 50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of similar to 100 eV. This adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars. Conclusions. Though showing similar rotational periods and being hard X-ray sources, these two intermediate polars appear different in several respects, among which the presence of a soft X-ray component in 1RXS J213344.1+510725. This source also emits circularly polarized light in the optical band, thus joining the group of soft and polarized intermediate polars as a fifth member. How the hard X-ray and polarized emission are thermalized in these systems is a timely question.
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ASTRONOMY & ASTROPHYSICS 501(3) 1047-1058 2009年7月Context. A significant number of cataclysmic variables have been detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type. Aims. We present a detailed X-ray broad-band study of two new sources, IGR J00234+6141 and 1RXS J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class. Methods. Timing and spectral analysis of IGR J00234+6141 are based on an XMM-Newton observation and INTEGRAL publicly available data. For 1RXS J213344.1+510725, we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data. Results. We determine a spin period of 561.64 +/- 0.56 s for the white dwarf in IGR J00234+6141. The X-ray pulses are observed up to similar to 2 keV. From XMM-Newton and Suzaku observations of 1RXS J213344.1+510725, we find a rotational period of 570.862 +/- 0.034 s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100 keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of similar to 50 keV. In 1RXS J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of similar to 100 eV. This adds 1RXS J213344.1+510725 to the growing group of soft X-ray intermediate polars. Conclusions. Though showing similar rotational periods and being hard X-ray sources, these two intermediate polars appear different in several respects, among which the presence of a soft X-ray component in 1RXS J213344.1+510725. This source also emits circularly polarized light in the optical band, thus joining the group of soft and polarized intermediate polars as a fifth member. How the hard X-ray and polarized emission are thermalized in these systems is a timely question.
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Publications of the Astronomical Society of Japan 61(2) 275-281 2009年4月
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(2) 275-281 2009年4月We searched for evidence of line emission around 4 keV from the northwestern rim of the supernova remnant RX J0852.0-4622 using Suzaku XIS data. Several papers have reported on the detection of an emission line around 4.1 keV from this region of the sky. This line Would arise from K-band fluorescence by Sc-44, the immediate decay product of Ti-44. We performed spectral analysis for the entire portion of the NW rim of the remnant within the XIS field of view, as well as various regions corresponding to regions of published claims of line emission. We found no line emission around 4.1 keV anywhere, and are able to set a restrictive Upper limit to the X-ray flux: 1.1 x 10(-6) s(-1) cm(-2) for the entire field. For every region, our flux upper limit falls below that of the previously claimed detection. Therefore, we conclude that, to date, no definite X-ray line feature from Sc-K emission has been detected in the NW rim of RX J0852.0-4622. Our negative-detection supports the recent claim that RX J0852-4622 is neither young (1700-4000 yr) nor nearby (similar to 750 pc).
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(2) 275-281 2009年4月We searched for evidence of line emission around 4 keV from the northwestern rim of the supernova remnant RX J0852.0-4622 using Suzaku XIS data. Several papers have reported on the detection of an emission line around 4.1 keV from this region of the sky. This line Would arise from K-band fluorescence by Sc-44, the immediate decay product of Ti-44. We performed spectral analysis for the entire portion of the NW rim of the remnant within the XIS field of view, as well as various regions corresponding to regions of published claims of line emission. We found no line emission around 4.1 keV anywhere, and are able to set a restrictive Upper limit to the X-ray flux: 1.1 x 10(-6) s(-1) cm(-2) for the entire field. For every region, our flux upper limit falls below that of the previously claimed detection. Therefore, we conclude that, to date, no definite X-ray line feature from Sc-K emission has been detected in the NW rim of RX J0852.0-4622. Our negative-detection supports the recent claim that RX J0852-4622 is neither young (1700-4000 yr) nor nearby (similar to 750 pc).
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(2) 275-281 2009年4月We searched for evidence of line emission around 4 keV from the northwestern rim of the supernova remnant RX J0852.0-4622 using Suzaku XIS data. Several papers have reported on the detection of an emission line around 4.1 keV from this region of the sky. This line Would arise from K-band fluorescence by Sc-44, the immediate decay product of Ti-44. We performed spectral analysis for the entire portion of the NW rim of the remnant within the XIS field of view, as well as various regions corresponding to regions of published claims of line emission. We found no line emission around 4.1 keV anywhere, and are able to set a restrictive Upper limit to the X-ray flux: 1.1 x 10(-6) s(-1) cm(-2) for the entire field. For every region, our flux upper limit falls below that of the previously claimed detection. Therefore, we conclude that, to date, no definite X-ray line feature from Sc-K emission has been detected in the NW rim of RX J0852.0-4622. Our negative-detection supports the recent claim that RX J0852-4622 is neither young (1700-4000 yr) nor nearby (similar to 750 pc).
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日本物理学会講演概要集 64(1) 93-93 2009年3月3日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S197-S207 2009年1月We report on Suzaku and Chandra observations of the young supernova remnant CTB 37 B, from which TeV gamma-rays were detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided us with a clear image of diffuse emission and high-quality spectra. The spectra revealed that the diffuse emission is comprised of thermal and non-thermal components. The thermal component can be represented by an NEI model with a temperature, a pre-shock electron density and an age of 0.9 +/- 0.2 keV, 0.4 +/- 0.1 cm(-3), and 650(-300)(+2500) yr, respectively. This suggests that the explosion of CTB 37 B occurred ill a low-density space. A non-thermal power-law component was found from the southern region of CTB 37 B. Its photon index of similar to 1.5 and a high roll-off energy (greater than or similar to 15 keV) indicate efficient cosmic-ray acceleration. A comparison of this X-ray spectrum with the TeV gamma-ray spectrum leads us to conclude that the TeV gamma-ray emission seems to be powered by either multi-zone Inverse Compton scattering or the decay of neutral pions. The point source resolved by Chandra near the shell is probably associated with CTB 37 B, because of the common hydrogen column density with the diffuse thermal emission. Spectral and temporal characteristics Suggest that this source is a new anomalous X-ray pulsar.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S77-S91 2009年1月We present results from the Suzaku observations of the dwarf nova SS Cyg in quiescence and outburst in 2005 November. The high sensitivity of the HXD PIN and the high spectral resolution of the XIS enabled us to determine the plasma parameters with unprecedented precision. The maximum temperature of the plasma in quiescence, 20.4(-2.6)(+4.0) (stat) +/- 3.0 (sys) keV, is significantly higher than that in outburst, 6.0(-1.3)(+0.2) keV. The elemental abundances are close to the solar ones for medium-Z elements (Si, S, Ar), whereas they decline both in lighter and heavier elements, except for that of carbon, which is 2 solar, at least. The solid angle of the reflector subtending over an optically thin thermal plasma is Omega(Q)/(2 pi) = 1.7 +/- 0.2 (stat) +/- 0.1 (sys) in quiescence. A 6.4 keV iron K alpha line is resolved into narrow and broad components. These facts indicate that both the white dwarf and the accretion disk contribute to the reflection. We consider the standard optically thin boundary layer as being the most plausible picture for the plasma configuration in quiescence. The solid angle of the reflector in outburst, Omega(O) (2 pi) = 0.9(-0.4)(+0.5), and a broad 6.4 keV iron line indicate that the reflection in outburst originates from the accretion disk and an equatorial accretion belt. The broad 6.4 keV line suggests that the optically thin thermal plasma is distributed on the accretion disk like solar corona.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S35-S53 2009年1月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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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S197-S207 2009年1月We report on Suzaku and Chandra observations of the young supernova remnant CTB 37 B, from which TeV gamma-rays were detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided us with a clear image of diffuse emission and high-quality spectra. The spectra revealed that the diffuse emission is comprised of thermal and non-thermal components. The thermal component can be represented by an NEI model with a temperature, a pre-shock electron density and an age of 0.9 +/- 0.2 keV, 0.4 +/- 0.1 cm(-3), and 650(-300)(+2500) yr, respectively. This suggests that the explosion of CTB 37 B occurred ill a low-density space. A non-thermal power-law component was found from the southern region of CTB 37 B. Its photon index of similar to 1.5 and a high roll-off energy (greater than or similar to 15 keV) indicate efficient cosmic-ray acceleration. A comparison of this X-ray spectrum with the TeV gamma-ray spectrum leads us to conclude that the TeV gamma-ray emission seems to be powered by either multi-zone Inverse Compton scattering or the decay of neutral pions. The point source resolved by Chandra near the shell is probably associated with CTB 37 B, because of the common hydrogen column density with the diffuse thermal emission. Spectral and temporal characteristics Suggest that this source is a new anomalous X-ray pulsar.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S17-S33 2009年1月Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10-600 keV, by utilizing PIN photodiodes and GSO scintillators; mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information, The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1 sigma systematic error is estimated to be less than 3% (PIN 15-40 keV) and 1% (GSO 50-100 keV) for more than 10 ks exposure.
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Publications of the Astronomical Society of Japan 61(Sp. Iss. 1) S167-172 2009年
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S197-S207 2009年1月We report on Suzaku and Chandra observations of the young supernova remnant CTB 37 B, from which TeV gamma-rays were detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided us with a clear image of diffuse emission and high-quality spectra. The spectra revealed that the diffuse emission is comprised of thermal and non-thermal components. The thermal component can be represented by an NEI model with a temperature, a pre-shock electron density and an age of 0.9 +/- 0.2 keV, 0.4 +/- 0.1 cm(-3), and 650(-300)(+2500) yr, respectively. This suggests that the explosion of CTB 37 B occurred ill a low-density space. A non-thermal power-law component was found from the southern region of CTB 37 B. Its photon index of similar to 1.5 and a high roll-off energy (greater than or similar to 15 keV) indicate efficient cosmic-ray acceleration. A comparison of this X-ray spectrum with the TeV gamma-ray spectrum leads us to conclude that the TeV gamma-ray emission seems to be powered by either multi-zone Inverse Compton scattering or the decay of neutral pions. The point source resolved by Chandra near the shell is probably associated with CTB 37 B, because of the common hydrogen column density with the diffuse thermal emission. Spectral and temporal characteristics Suggest that this source is a new anomalous X-ray pulsar.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S77-S91 2009年1月We present results from the Suzaku observations of the dwarf nova SS Cyg in quiescence and outburst in 2005 November. The high sensitivity of the HXD PIN and the high spectral resolution of the XIS enabled us to determine the plasma parameters with unprecedented precision. The maximum temperature of the plasma in quiescence, 20.4(-2.6)(+4.0) (stat) +/- 3.0 (sys) keV, is significantly higher than that in outburst, 6.0(-1.3)(+0.2) keV. The elemental abundances are close to the solar ones for medium-Z elements (Si, S, Ar), whereas they decline both in lighter and heavier elements, except for that of carbon, which is 2 solar, at least. The solid angle of the reflector subtending over an optically thin thermal plasma is Omega(Q)/(2 pi) = 1.7 +/- 0.2 (stat) +/- 0.1 (sys) in quiescence. A 6.4 keV iron K alpha line is resolved into narrow and broad components. These facts indicate that both the white dwarf and the accretion disk contribute to the reflection. We consider the standard optically thin boundary layer as being the most plausible picture for the plasma configuration in quiescence. The solid angle of the reflector in outburst, Omega(O) (2 pi) = 0.9(-0.4)(+0.5), and a broad 6.4 keV iron line indicate that the reflection in outburst originates from the accretion disk and an equatorial accretion belt. The broad 6.4 keV line suggests that the optically thin thermal plasma is distributed on the accretion disk like solar corona.
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Publications of the Astronomical Society of Japan 61 S35-S53 2009年
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S197-S207 2009年1月We report on Suzaku and Chandra observations of the young supernova remnant CTB 37 B, from which TeV gamma-rays were detected by the H.E.S.S. Cherenkov telescope. The 80 ks Suzaku observation provided us with a clear image of diffuse emission and high-quality spectra. The spectra revealed that the diffuse emission is comprised of thermal and non-thermal components. The thermal component can be represented by an NEI model with a temperature, a pre-shock electron density and an age of 0.9 +/- 0.2 keV, 0.4 +/- 0.1 cm(-3), and 650(-300)(+2500) yr, respectively. This suggests that the explosion of CTB 37 B occurred ill a low-density space. A non-thermal power-law component was found from the southern region of CTB 37 B. Its photon index of similar to 1.5 and a high roll-off energy (greater than or similar to 15 keV) indicate efficient cosmic-ray acceleration. A comparison of this X-ray spectrum with the TeV gamma-ray spectrum leads us to conclude that the TeV gamma-ray emission seems to be powered by either multi-zone Inverse Compton scattering or the decay of neutral pions. The point source resolved by Chandra near the shell is probably associated with CTB 37 B, because of the common hydrogen column density with the diffuse thermal emission. Spectral and temporal characteristics Suggest that this source is a new anomalous X-ray pulsar.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S17-S33 2009年1月Suzaku Hard X-ray Detector (HXD) achieved the lowest background level than any other previously or currently operational missions sensitive in the energy range of 10-600 keV, by utilizing PIN photodiodes and GSO scintillators; mounted in BGO active shields to reject particle background and Compton-scattered events as much as possible. Because it does not have an imaging capability nor rocking mode for the background monitor, the sensitivity is limited by the reproducibility of the non X-ray background (NXB) model. We modeled the HXD NXB, which varies with time as well as other satellites with a low-Earth orbit, by utilizing several parameters, including particle monitor counts and satellite orbital/attitude information, The model background is supplied as an event file in which the background events are generated by random numbers, and can be analyzed in the same way as the real data. The reproducibility of the NXB model depends on the event selection criteria (such as cut-off rigidity and energy band) and the integration time, and the 1 sigma systematic error is estimated to be less than 3% (PIN 15-40 keV) and 1% (GSO 50-100 keV) for more than 10 ks exposure.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(Sp. Iss. 1) S167-S174 2009年1月Tycho's supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26-29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with a photon index of 2.7 and a thermal bremsstrahlung model with a temperature of 4.7 keV. The former component can alternatively be modeled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K alpha line (6.445 keV), we observed for the first time significant K alpha line emission from trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K beta lines from Ca (4.56 keV) and Fe (7.11 keV) were also seen. The ionization states of Cr and Mn, based on their line centroids, Lire estimated to be similar to that of Fe K alpha (Fe XV or XVI).
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日本物理学会講演概要集 63(2) 89-89 2008年8月25日
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(2) 387-397 2008年4月A fast rotating magnetized white dwarf, AE Aquarii, was observed with Suzaku, in 2005 October-November and 2006 October with exposures of 53.1 and 42.4ks, respectively. In addition to clear spin modulation in the 0.5-10 keV band of the XIS data at the barycentric period of 33.0769 +/- 0.0001 s, the 10-30 keV HXD data in the second half of the 2005 observation also showed statistically significant periodic signals at a consistent period. On that occasion, the spin-folded HXD light curve exhibited two sharp spikes separated by similar to 0.2 cycles in phase, in contrast to approximately sinusoidal profiles observed at energies below similar to 4 keV. The folded 4-10 keV XIS light curves are understood to be a superposition of those two types of pulse profiles. The phase-averaged 1.5-10 keV spectra can be reproduced by two thermal components with temperatures of 2.0(-0.16)(+0.20) keV and 0.53(-0.13)(+0.14) keV but the 12-25 keV HXD data show a significant excess above the extrapolated model. This excess can be explained by either a power-law model with a photon index of 1.12(-0.62)(+0.63) or a third thermal component with a temperature of 54(-47)(+26) keV. At a distance of 102pc, the 4-30keV luminosities of the thermal and the additional components become 1.7(-0.6)(+1.3) and 5.3(-0.3)(+15.3) X 10(29) erg s(-1), respectively. The latter corresponds to 0.09% of the spin-down energy of the object. Possible emission mechanisms of the hard pulsations are discussed, including non-thermal ones, in particular.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(2) 237-244 2008年4月A Suzaku TOO observation of CXOU J164710.2-455216 was performed on 2006 September 23-24 for a net exposure of 38.8 ks. Pulsations were clearly detected in the XIS light curves with a pulse period of 10.61063(2) s. The XIS pulse profile is found to be highly non-sinusoidal. It shows 3 peaks of different amplitudes with an RMS fractional amplitude of similar to 11% in the 0.2-6.0 keV energy band. The 1 -10 keV XIS spectra were well fitted by two different models consisting of a power-law and a blackbody component and two blackbody components, respectively. Although both the models are statistically acceptable, a difference in the pulse profiles at soft (0.2-6.0 keV) and hard (6-12keV) X-rays favors the model consisting of two blackbody components. The temperatures of two blackbody components are found to be 0.61 +/- 0.01 keV and 1.22 +/- 0.06 keV, and the value of the absorption column density is 1.73 +/- 0.03 x 10(22) atoms cm(-2). Pulse phase resolved spectroscopy shows that the flux of the soft blackbody component consists of three narrow peaks, whereas the flux of the other component shows a single peak over the pulse period of the AXP. The blackbody radii change between 2.2-2.7 km and 0.28-0.38 km (assuming the source distance to be 5 kpc) over the pulse phases for the soft and hard components, respectively. The details of the results obtained from the timing and spectral analyses are presented.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(2) 387-397 2008年4月A fast rotating magnetized white dwarf, AE Aquarii, was observed with Suzaku, in 2005 October-November and 2006 October with exposures of 53.1 and 42.4ks, respectively. In addition to clear spin modulation in the 0.5-10 keV band of the XIS data at the barycentric period of 33.0769 +/- 0.0001 s, the 10-30 keV HXD data in the second half of the 2005 observation also showed statistically significant periodic signals at a consistent period. On that occasion, the spin-folded HXD light curve exhibited two sharp spikes separated by similar to 0.2 cycles in phase, in contrast to approximately sinusoidal profiles observed at energies below similar to 4 keV. The folded 4-10 keV XIS light curves are understood to be a superposition of those two types of pulse profiles. The phase-averaged 1.5-10 keV spectra can be reproduced by two thermal components with temperatures of 2.0(-0.16)(+0.20) keV and 0.53(-0.13)(+0.14) keV but the 12-25 keV HXD data show a significant excess above the extrapolated model. This excess can be explained by either a power-law model with a photon index of 1.12(-0.62)(+0.63) or a third thermal component with a temperature of 54(-47)(+26) keV. At a distance of 102pc, the 4-30keV luminosities of the thermal and the additional components become 1.7(-0.6)(+1.3) and 5.3(-0.3)(+15.3) X 10(29) erg s(-1), respectively. The latter corresponds to 0.09% of the spin-down energy of the object. Possible emission mechanisms of the hard pulsations are discussed, including non-thermal ones, in particular.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(2) 237-244 2008年4月A Suzaku TOO observation of CXOU J164710.2-455216 was performed on 2006 September 23-24 for a net exposure of 38.8 ks. Pulsations were clearly detected in the XIS light curves with a pulse period of 10.61063(2) s. The XIS pulse profile is found to be highly non-sinusoidal. It shows 3 peaks of different amplitudes with an RMS fractional amplitude of similar to 11% in the 0.2-6.0 keV energy band. The 1 -10 keV XIS spectra were well fitted by two different models consisting of a power-law and a blackbody component and two blackbody components, respectively. Although both the models are statistically acceptable, a difference in the pulse profiles at soft (0.2-6.0 keV) and hard (6-12keV) X-rays favors the model consisting of two blackbody components. The temperatures of two blackbody components are found to be 0.61 +/- 0.01 keV and 1.22 +/- 0.06 keV, and the value of the absorption column density is 1.73 +/- 0.03 x 10(22) atoms cm(-2). Pulse phase resolved spectroscopy shows that the flux of the soft blackbody component consists of three narrow peaks, whereas the flux of the other component shows a single peak over the pulse period of the AXP. The blackbody radii change between 2.2-2.7 km and 0.28-0.38 km (assuming the source distance to be 5 kpc) over the pulse phases for the soft and hard components, respectively. The details of the results obtained from the timing and spectral analyses are presented.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(Sp. Iss. 1) S25-S33 2008年2月The hard X-ray detector (HXD) aboard the X-ray satellite Suzaku is designed to have a good timing capability with a 61 its time resolution. In addition to detailed descriptions of the HXD timing system, results of in-orbit timing calibration and the performance of the HXD are summarized. The relative accuracy of time measurements of the HXD event was confirmed to have an accuracy of 1.9 x 10(-9) s s(-1) per day, and the absolute timing was confirmed to be accurate to 360 mu s or better. The results were achieved mainly through observations of the Crab pulsar, including simultaneous ones with RXTE, INTEGRAL, and Swift.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(Sp. Iss. 1) S57-S68 2008年2月The accretion-powered pulsar Her X-1 was observed with Suzaku twice in its main-on state, on 2005 October 5-6 and 2006 March 29-30, for a net exposure of 30.5 ks and 34.4 ks, respectively. In the 2005 and 2006 observations, the source was detected at an average 10-30 keV intensity of 290 mCrab and 230 mCrab, respectively. The intrinsic pulse period was measured on both occasions at 1.23776 s by HXD-PIN, after barycentric and binary corrections. The pulse phase-averaged spectra in the energy range above 10 keV were well fitted by the "Negative and Positive power-law times EXponential" (NPEX) model, multiplied by a fundamental cyclotron resonance scattering feature at similar to 36 keV, which appears very significantly in the HXD-PIN data. The resonance profiles were successfully reproduced by a Lorentzian-type scattering cross section, rather than by a Gaussian-type alternative. The pulse phase-averaged HXD-GSO data, covering 50-120 keV, are featureless. However, in a differential spectrum between the pulse-decay phase and off-pulse phase, the second-harmonic cyclotron resonance was detected in the GSO data at similar to 73 keV, with a depth of 1.6(-0.7)(+0.9) This makes Her X-1 a 6th pulsar with established second-harmonic resonance. The implications of these results are briefly discussed.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60(Sp. Iss. 1) S361-S373 2008年2月We have performed a joint analysis of prompt emission from four bright short gamma-ray bursts (GRBs) with the Suzaku-WAM and the Konus-Wind experiments. This joint analysis allows us to investigate the spectral properties of short-duration bursts over a wider energy band with a higher accuracy. We find that these bursts have a high E-peak, around 1 MeV and have a harder power-law component than that of long GRBs. However, we can not determine whether these spectra follow the cut-off power-law model or the Band model. We also investigated the spectral lag, hardness ratio, inferred isotropic radiation energy and existence of a soft emission hump, in order to classify them into short or long GRBs using several criteria, in addition to the burst duration. We find that all criteria, except for the existence of the soft hump, support the fact that our four GRB samples are correctly classified as belonging to the short class. In addition, our broad-band analysis revealed that there is no evidence of GRBs with a very large hardness ratio, as seen in the BATSE short GRB sample, and that the spectral lag of our four short GRBs is consistent with zero, even in the MeV energy band, unlike long GRBs. Although our short GRB samples are still limited, these results suggest that the spectral hardness of short GRBs might not differ significantly from that of long GRBs, and also that the spectral lag at high energies could be a strong criterion for burst classification.
講演・口頭発表等
36共同研究・競争的資金等の研究課題
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