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
2-
2007年
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1999年
論文
181-
Geophysical Research Letters 2024年8月29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
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Space Telescopes and Instrumentation 2024: Ultraviolet to Gamma Ray 60-60 2024年8月21日
MISC
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61(2) 201-211 2009年4月We performed a time-resolved spectral analysis of a bright, long gamma-ray burst GRB 061007 using Suzaku/WAM and Swift/BAT. Because of the large effective area of the WAM, we can investigate the time evolution of the spectral peak energy E-peak(t) and the luminosity L-iso(t) with 1-s time resolution, and we find that the time-resolved pulses also satisfy the E-peak-L-iso relation, which was found for the time-averaged spectra of other bursts, suggesting the same physical conditions in each pulse. Furthermore, the initial rising phase of each pulse could be an outlier of this relation with higher E-peak(t) Value by a factor of 2. This difference could Suggest that the fireball radius expands by a factor of 2-4 and / or bulk Lorentz factor of the fireball is decelerated by a factor of similar to 4 during the initial phase, providing a new probe of fireball dynamics in real time.
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日本物理学会講演概要集 64(1) 92-92 2009年3月3日
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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(2) 201-211 2009年
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S387-S393 2009年1月Spectral and timing studies of Suzaku ToO observations of two SGRs, 1900+14 and 1806-20, are presented. The X-ray quiescent emission spectra were well fitted by a two blackbody function, or a blackbody plus a power-law model. The non-thermal hard component discovered by INTEGRAL was detected by PIN diodes and its spectrum was reproduced by the power-law model reported by INTEGRAL. The XIS detected a periodicity of P = 5.1998 +/- 0.0002s for SGR 1900+14 and P = 7.6022 +/- 0.0007s for SGR 1806-20. The pulsed fraction was related to the burst activity for SGR 1900+14.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S327-S335 2009年1月An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with Suzaku is reported. Since Feigelson et al. (1995, ApJ, 449, L149) and Kaneda et al.(1995, AN, 453, L13) discovered the cosmic microwave background boosted inverse-Comptonized (IC) X-rays from the radio lobe, the magnetic field and electron energy density in the lobes have been estimated under the assumption that a single component of the relativistic electrons generates both the IC X-rays and the synchrotron radio emission. However, electrons generating the observed IC X-rays in the 1-10 keV band do not possess sufficient energy to radiate the observed synchrotron radio emission under the estimated magnetic field of a few mu G. On the basis of observations made with Suzaku, we show in the present paper that a 0.7-20 keV spectrum is well described by a single power-law model with an energy index of 0.68 and a flux density of 0.12 +/- 0.01 nJy at 1 keV from the West lobe. The derived multiwavelength spectrum strongly suggests that a single electron energy distribution over a Lorentz factor gamma = 300-90000 is responsible for generating both the X-ray and radio emissions. The derived physical quantities are not only consistent with those reported for the West lobe, but are also in very good agreement with those reported for the East lobe.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S387-S393 2009年1月Spectral and timing studies of Suzaku ToO observations of two SGRs, 1900+14 and 1806-20, are presented. The X-ray quiescent emission spectra were well fitted by a two blackbody function, or a blackbody plus a power-law model. The non-thermal hard component discovered by INTEGRAL was detected by PIN diodes and its spectrum was reproduced by the power-law model reported by INTEGRAL. The XIS detected a periodicity of P = 5.1998 +/- 0.0002s for SGR 1900+14 and P = 7.6022 +/- 0.0007s for SGR 1806-20. The pulsed fraction was related to the burst activity for SGR 1900+14.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 61 S327-S335 2009年1月An observation of the West lobe of radio galaxy Fornax A (NGC 1316) with Suzaku is reported. Since Feigelson et al. (1995, ApJ, 449, L149) and Kaneda et al.(1995, AN, 453, L13) discovered the cosmic microwave background boosted inverse-Comptonized (IC) X-rays from the radio lobe, the magnetic field and electron energy density in the lobes have been estimated under the assumption that a single component of the relativistic electrons generates both the IC X-rays and the synchrotron radio emission. However, electrons generating the observed IC X-rays in the 1-10 keV band do not possess sufficient energy to radiate the observed synchrotron radio emission under the estimated magnetic field of a few mu G. On the basis of observations made with Suzaku, we show in the present paper that a 0.7-20 keV spectrum is well described by a single power-law model with an energy index of 0.68 and a flux density of 0.12 +/- 0.01 nJy at 1 keV from the West lobe. The derived multiwavelength spectrum strongly suggests that a single electron energy distribution over a Lorentz factor gamma = 300-90000 is responsible for generating both the X-ray and radio emissions. The derived physical quantities are not only consistent with those reported for the West lobe, but are also in very good agreement with those reported for the East lobe.
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ASTROPHYSICAL JOURNAL 688(1) 491-498 2008年11月The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-Wind, RHESSI, Suzaku WAM, and Swift BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multipeaked emission over a period of about 1 minute. The total burst fluence as observed by Konus is 1: 79; 10(-4) ergs cm(-2) (20 keV-10 MeV). Using the spectroscopic redshift z = 1.548, we find that the burst is consistent with the "Amati'' E-peak,(i)-E-iso correlation. Assuming a jet opening angle derived from broadband modeling of the burst afterglow, GRB 070125 is a significant outlier to the "Ghirlanda'' E-peak,(i)-E-gamma correlation. Its collimation-corrected energy release, E-gamma = 2.5 x 10(52) ergs, is the largest yet observed.
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ASTROPHYSICAL JOURNAL 688(1) 491-498 2008年11月The long, bright gamma-ray burst GRB 070125 was localized by the Interplanetary Network. We present light curves of the prompt gamma-ray emission as observed by Konus-Wind, RHESSI, Suzaku WAM, and Swift BAT. We detail the results of joint spectral fits with Konus and RHESSI data. The burst shows moderate hard-to-soft evolution in its multipeaked emission over a period of about 1 minute. The total burst fluence as observed by Konus is 1: 79; 10(-4) ergs cm(-2) (20 keV-10 MeV). Using the spectroscopic redshift z = 1.548, we find that the burst is consistent with the "Amati'' E-peak,(i)-E-iso correlation. Assuming a jet opening angle derived from broadband modeling of the burst afterglow, GRB 070125 is a significant outlier to the "Ghirlanda'' E-peak,(i)-E-gamma correlation. Its collimation-corrected energy release, E-gamma = 2.5 x 10(52) ergs, is the largest yet observed.
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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 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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S351-S360 2008年2月We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the Swift/BAT and Swift/XRT +004 data. The observed spectra were fit by power-law photon indices which rapidly changed from Gamma = (+1.51)(-0.03) to Gamma = 5.30(-0.59)(+0.69) within a few hundred seconds. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron-acceleration and synchrotron -radiation processes. We then applied an alternative broken power-law with exponential cutoff (BPEC) model. It is valid to consider the exponential shape is equivalent to a synchrotron cutoff. Since the spectral cutoff appears in the soft X-ray band, we conclude that the electron acceleration must be inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the end of the prompt tail. After that, typical afterglow spectra with F = 2.0 have been continuously and preciously monitored by both Swift/XRT and Suzaku/XIS. We could successfully trace the temporal history of two characteristic break energies that have a time dependence of (proportional to t(-3)-t(-4), while the following afterglow spectra are quite stable. This fact indicates that the emitting material of the prompt tail is due to completely different dynamics from the shallow decay component. Therefore, the emission sites of two distinct phenomena obviously differ from each other.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 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 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.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 S351-S360 2008年2月We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku satellites. We found rapid spectral softening during both the prompt tail phase and the decline phase of an X-ray flare in the Swift/BAT and Swift/XRT +004 data. The observed spectra were fit by power-law photon indices which rapidly changed from Gamma = (+1.51)(-0.03) to Gamma = 5.30(-0.59)(+0.69) within a few hundred seconds. This is one of the steepest X-ray spectra ever observed, making it quite difficult to explain by simple electron-acceleration and synchrotron -radiation processes. We then applied an alternative broken power-law with exponential cutoff (BPEC) model. It is valid to consider the exponential shape is equivalent to a synchrotron cutoff. Since the spectral cutoff appears in the soft X-ray band, we conclude that the electron acceleration must be inefficient in the internal shocks of GRB 060904A. These cutoff spectra suddenly disappeared at the end of the prompt tail. After that, typical afterglow spectra with F = 2.0 have been continuously and preciously monitored by both Swift/XRT and Suzaku/XIS. We could successfully trace the temporal history of two characteristic break energies that have a time dependence of (proportional to t(-3)-t(-4), while the following afterglow spectra are quite stable. This fact indicates that the emitting material of the prompt tail is due to completely different dynamics from the shallow decay component. Therefore, the emission sites of two distinct phenomena obviously differ from each other.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 60 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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ASTROPHYSICAL JOURNAL 668(2) L95-L98 2007年10月We study the "normal" decay phase of the X- ray afterglows of gamma- ray bursts ( GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R band. The classical external- shock model - in which neither the delayed energy injection nor time dependency of shock microphysics is considered shows that the decay indices of the X- ray and R- band light curves, alpha(x) and alpha(o), obey a certain relation, and that in particular, alpha(o) - alpha(x) should be larger than -1/4 unless the ambient density increases with the distance from the central engine. For our selected 14 samples, we have found that four events violate the limit at more than the 3 sigma level, so that a fraction of events are outliers of the classical external-shock model at the "normal" decay phase.
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ASTROPHYSICAL JOURNAL 668(2) L95-L98 2007年10月We study the "normal" decay phase of the X- ray afterglows of gamma- ray bursts ( GRBs), which follows the shallow decay phase, using the events simultaneously observed in the R band. The classical external- shock model - in which neither the delayed energy injection nor time dependency of shock microphysics is considered shows that the decay indices of the X- ray and R- band light curves, alpha(x) and alpha(o), obey a certain relation, and that in particular, alpha(o) - alpha(x) should be larger than -1/4 unless the ambient density increases with the distance from the central engine. For our selected 14 samples, we have found that four events violate the limit at more than the 3 sigma level, so that a fraction of events are outliers of the classical external-shock model at the "normal" decay phase.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(4) L29-L33 2007年8月Observations were made of the optical afterglow of GRB 051028 with the Lulin observatory 1.0 m telescope and the Wide-Field Telescope for GRB Early Timing (WIDGET) robotic telescope system. R-band photometric data were obtained on 2005 October 28 (UT), or 0.095-0.180 d after the burst. There is a possible plateau in the optical light curve around 0.1 d after the burst; the afterglow of GRB 051028 resembles optically bright afterglows (e.g., GRB 041006, GRB 050319, GRB 060605) in shape of the light curve, but not in brightness. The brightness of the GRB 051028 afterglow is 3 mag fainter than that of one of the dark events, GRB 020124. Optically dark GRBs have been attributed to dust extinction within the host galaxy or a high redshift. However, a spectrum analysis of the X-rays implies that there is no significant absorption by the host galaxy. Furthermore, according to a theoretical calculation of the Ly alpha absorption to find the limit of the GRB 051028's redshift, the expected R-band absorption is not high enough to explain the darkness of the afterglow. The present results disfavor either the high-redshift hypothesis or the high-extinction scenario for optically dark bursts; rather, they are consistent with the possibility that the brightness of the optical afterglow is intrinsically dark.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(4) L29-L33 2007年8月Observations were made of the optical afterglow of GRB 051028 with the Lulin observatory 1.0 m telescope and the Wide-Field Telescope for GRB Early Timing (WIDGET) robotic telescope system. R-band photometric data were obtained on 2005 October 28 (UT), or 0.095-0.180 d after the burst. There is a possible plateau in the optical light curve around 0.1 d after the burst; the afterglow of GRB 051028 resembles optically bright afterglows (e.g., GRB 041006, GRB 050319, GRB 060605) in shape of the light curve, but not in brightness. The brightness of the GRB 051028 afterglow is 3 mag fainter than that of one of the dark events, GRB 020124. Optically dark GRBs have been attributed to dust extinction within the host galaxy or a high redshift. However, a spectrum analysis of the X-rays implies that there is no significant absorption by the host galaxy. Furthermore, according to a theoretical calculation of the Ly alpha absorption to find the limit of the GRB 051028's redshift, the expected R-band absorption is not high enough to explain the darkness of the afterglow. The present results disfavor either the high-redshift hypothesis or the high-extinction scenario for optically dark bursts; rather, they are consistent with the possibility that the brightness of the optical afterglow is intrinsically dark.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(2) 279-297 2007年4月We report on deep (40 ks x 4) observations of the bright broad line radio galaxy 3C 120 using Suzaku. The observations were spaced one week apart, and sampled a range of continuum fluxes. An excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50 keV) within each 40 ks exposure. We clearly resolved the iron K emission-line complex, finding that it consists of a narrow K alpha core (sigma similar or equal to 110 eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broadline is iron Kline emission from a face-on accretion disk that is truncated at similar to 10 r(g). Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of R similar or equal to 0.6), superposed on the primary X-ray continuum of Gamma similar or equal to 1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C 120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of Gamma similar or equal to 2.7, possibly related to non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59(2) 279-297 2007年4月We report on deep (40 ks x 4) observations of the bright broad line radio galaxy 3C 120 using Suzaku. The observations were spaced one week apart, and sampled a range of continuum fluxes. An excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50 keV) within each 40 ks exposure. We clearly resolved the iron K emission-line complex, finding that it consists of a narrow K alpha core (sigma similar or equal to 110 eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broadline is iron Kline emission from a face-on accretion disk that is truncated at similar to 10 r(g). Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of R similar or equal to 0.6), superposed on the primary X-ray continuum of Gamma similar or equal to 1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C 120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of Gamma similar or equal to 2.7, possibly related to non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects.
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ASTROPHYSICAL JOURNAL 657(1) 359-366 2007年3月We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations: GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in the pre-Swift era. However, we find that the X-ray afterglow light curves, which extend up to 10-70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow light curves in our sample satisfy the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen for some unknown reason.
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ASTROPHYSICAL JOURNAL 657(1) 359-366 2007年3月We analyze Swift gamma-ray bursts (GRBs) and X-ray afterglows for three GRBs with spectroscopic redshift determinations: GRB 050401, XRF 050416a, and GRB 050525a. We find that the relation between spectral peak energy and isotropic energy of prompt emissions (the Amati relation) is consistent with that for the bursts observed in the pre-Swift era. However, we find that the X-ray afterglow light curves, which extend up to 10-70 days, show no sign of the jet break that is expected in the standard framework of collimated outflows. We do so by showing that none of the X-ray afterglow light curves in our sample satisfy the relation between the spectral and temporal indices that is predicted for the phase after jet break. The jet break time can be predicted by inverting the tight empirical relation between the peak energy of the spectrum and the collimation-corrected energy of the prompt emission (the Ghirlanda relation). We find that there are no temporal breaks within the predicted time intervals in X-ray band. This requires either that the Ghirlanda relation has a larger scatter than previously thought, that the temporal break in X-rays is masked by some additional source of X-ray emission, or that it does not happen for some unknown reason.
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日本物理学会講演概要集 62(1) 95-95 2007年2月28日
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日本物理学会講演概要集 62(1) 95-95 2007年2月28日
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日本物理学会講演概要集 62(1) 103-103 2007年2月28日
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ASTRONOMY & ASTROPHYSICS 462(3) L57-U9 2007年2月Aims. Understand the shape and implications of the multiband ligth curve of GRB050408, an X-ray rich (XRR) burst. Methods. We present a multiband optical light curve, covering the time from the onset of the.-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date. Results. The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.
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ASTRONOMY & ASTROPHYSICS 462(3) L57-U9 2007年2月Aims. Understand the shape and implications of the multiband ligth curve of GRB050408, an X-ray rich (XRR) burst. Methods. We present a multiband optical light curve, covering the time from the onset of the.-ray event to several months after, when we only detect the host galaxy. Together with X-ray, millimetre and radio observations we compile what, to our knowledge, is the most complete multiband coverage of an XRR burst afterglow to date. Results. The optical and X-ray light curve is characterised by an early flattening and an intense bump peaking around 6 days after the burst onset. We explain the former by an off-axis viewed jet, in agreement with the predictions made for XRR by some models, and the latter with an energy injection equivalent in intensity to the initial shock. The analysis of the spectral flux distribution reveals an extinction compatible with a low chemical enrichment surrounding the burst. Together with the detection of an underlying starburst host galaxy we can strengthen the link between XRR and classical long-duration bursts.
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日本物理学会講演概要集 62 106-106 2007年
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S1-S7 2007年1月High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S361-S367 2007年1月Results are presented of early X-ray afterglow observations of GRB 060105 by Swift and Suzaku. The bright, long gamma-ray burst GRB; 060105 triggered the Swift Burst Alert Telescope at 06:49:28 on 2006 January 5 (T-0). The Suzaku team commenced a pre-planned target of opportunity observation at 19 ks (5.3 hr) after the Swift trigger. The X-ray flux faded during observations from 6.8 x 10(-9) ergs(-1) cm(-2) (at T-0 + 87 s with the Swift/XRT) to 1.5 x 10(-13) erg s(-1) cm(-2) [at T-0 + 94-101 ks with the Suzaku X-ray Imaging Spectrometer (XIS)] in the 2-10 keV energy band. Following prompt emission and successive very steep decay, a shallow decay was observed from To + 187 s to T-0 + 1287 s. After an observation gap during T-0 + (1.5-3) ks, an extremely early steep decay was observed in T-0 + (4-30) ks. The lightcurve flattened again at T-0 + 30ks, and another steep decay followed from T-0 + 50ks to the end of observations. Both steep decays exhibited decay indices of 2.3-2.4. This very early break, if it is a jet break, is the earliest case among X-ray afterglow observations, suggesting a very narrow jet whose opening angle is well below 1 degrees. The unique Suzaku/XIS data allow us to set very tight upper limits on line emission or absorption in this GRB. For the reported pseudo-redshift of z = 4.0 +/- 1.3 the upper limit on the iron line equivalent width is 50 eV.
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ASTROPHYSICAL JOURNAL 654(1) L25-L28 2007年1月Multiwavelength observations of the optical afterglow of GRB 050319 were performed from 1.31 to 9.92 hr after the burst. Our R-band light curves, combined with other published data, can be described by the smooth broken power-law function, with alpha(1) = -0.84 +/- 0.02 to alpha(2) = -0.48 +/- 0.03, 0.04 days after the gamma-ray burst. The optical light curves are characterized by shallow decays - as was also observed in the X-rays - which may have a similar origin, related to energy injection. However, our observations indicate that there is still a puzzle concerning the chromatic breaks in the R-band light curve (at 0.04 days) and the X-ray light curve (at 0.004 days) that remains to be solved.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S53-S76 2007年1月The in-orbit performance and calibration of the Hard X-ray Detector (HXD) on board the X-ray astronomy satellite Suzaku are described. Its basic performances, including a wide energy bandpass of 10-600keV, energy resolutions of similar to 4 keV (FWHM) at 40 keV and similar to 11% at 511 keV, and a high background rejection efficiency, have been confirmed by extensive in-orbit calibrations. The long-term gains of PIN-Si diodes have been stable within 1% for half a year, and those of scintillators have decreased by 5-20%. The residual non-X-ray background of the HXD is the lowest among past non-imaging hard X-ray instruments in energy ranges of 15-70 and 150-500 keV. We provide accurate calibrations of energy responses, angular responses, timing accuracy of the HXD, and relative normalizations to the X-ray CCD cameras using multiple observations of the Crab Nebula.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S35-S51 2007年1月The Hard X-ray Detector (HXD) on board Suzaku covers a wide energy range from 10 keV to 600 keV by the combination of silicon PIN diodes and GSO scintillators. The HXD is designed to achieve an extremely low in-orbit background based on a combination of new techniques, including the concept of a well-type active shield counter. With an effective area of 142 cm(2) at 20 keV and 273 cm(2) at 150 keV, the background level at sea level reached similar to 1 X 10(-5) cts s(-1) cm(-2) keV(-1) at 30 keV for the PIN diodes, and similar to 2 X 10(-5) cts s(-1) cm(-2) keV(-1) at 100 keV, and similar to 7 X 10(-6) cts s(-1) cm(-2) keV(-1) at 200 keV for the phoswich counter. Tight active shielding of the HXD results in a large array of guard counters surrounding the main detector parts. These anti-coincidence counters, made of similar to 4 cm thick BGO crystals, have a large effective area for sub-MeV to MeV gamma-rays. They work as an excellent gamma-ray burst monitor with limited angular resolution (similar to 5 degrees). The on-board signal-processing system and the data transmitted to the ground are also described.
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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 59 S1-S7 2007年1月High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.
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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日本学術振興会 科学研究費助成事業 2020年7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 2015年4月 - 2018年3月
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日本学術振興会 科学研究費助成事業 2010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 2008年 - 2008年
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日本学術振興会 科学研究費助成事業 2006年 - 2008年
