田代 信

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.

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.

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.

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.

The Japanese X-ray astronomical satellite Suzaku launched in July 2005 is equipped with two kinds of X-ray instruments for the wide-band spectroscopy. The X-ray CCD cameras (XIS) cover 0.3 to 12 keV with the energy resolution of 120eV at 6keV. The Hard X-ray Detector (HXD) consisting of well-type phoswitch counters covers 40-600keV. With these instruments, we organized a team for quick follow-up observations of gamma-ray bursts, aiming to observe the afterglow phase transition and to search for spectral features with the wide band X-ray instruments.

Even with the renaissance in gamma-ray burst (GRB) research fostered by the Swift satellite, few bursts have both contemporaneous observations at long wavelengths and exquisite observations at later times across the electromagnetic spectrum. We present here contemporaneous imaging with the KAIT robotic optical telescope, dense optical sampling with Lulin, supplemented with infrared data from PAIRITEL and radio to gamma-ray data from the literature. For the first time, we can test the constancy of microphysical parameters in the internal-external shock paradigm and carefully trace the flow of energy from the GRB to the surrounding medium. KAIT data taken P1 minute after the start of GRB 051111 and coinciding with the fading gamma-ray tail of the prompt emission indicate a smooth reinjection of energy into the shock. No color change is apparent in observations beginning similar to 1.5 minutes after the GRB and lasting for the first hour after the burst. There are achromatic flux modulations about the best-fit model at late (t approximate to 10(4) s) times, possibly due to variations in the external density. We find that the host galaxy extinction is well fit by a curve similar to that of the Small Magellanic Cloud. Low visual extinction, A(V) approximate to 0.2 mag, combined with high column densities determined from the X-ray and optical spectroscopy (N-H > 10(21) cm(-2)), indicate a low dust-to-metals ratio and a possible overabundance of the light metals. An apparent small ratio of total to selective extinction (R-V approximate to 2) argues against dust destruction by the GRB. Time constancy of both the IR/optical/UV spectral energy distribution and the soft X-ray absorption suggests that the absorbing material is not local to the GRB.

The Japanese X-ray astronomical satellite Suzaku launched in July 2005 is equipped with two kinds of X-ray instruments for the wide-band spectroscopy. The X-ray CCD cameras (XIS) cover 0.3 to 12 keV with the energy resolution of 120eV at 6keV. The Hard X-ray Detector (HXD) consisting of well-type phoswitch counters covers 40-600keV. With these instruments, we organized a team for quick follow-up observations of gamma-ray bursts, aiming to observe the afterglow phase transition and to search for spectral features with the wide band X-ray instruments.

Even with the renaissance in gamma-ray burst (GRB) research fostered by the Swift satellite, few bursts have both contemporaneous observations at long wavelengths and exquisite observations at later times across the electromagnetic spectrum. We present here contemporaneous imaging with the KAIT robotic optical telescope, dense optical sampling with Lulin, supplemented with infrared data from PAIRITEL and radio to gamma-ray data from the literature. For the first time, we can test the constancy of microphysical parameters in the internal-external shock paradigm and carefully trace the flow of energy from the GRB to the surrounding medium. KAIT data taken P1 minute after the start of GRB 051111 and coinciding with the fading gamma-ray tail of the prompt emission indicate a smooth reinjection of energy into the shock. No color change is apparent in observations beginning similar to 1.5 minutes after the GRB and lasting for the first hour after the burst. There are achromatic flux modulations about the best-fit model at late (t approximate to 10(4) s) times, possibly due to variations in the external density. We find that the host galaxy extinction is well fit by a curve similar to that of the Small Magellanic Cloud. Low visual extinction, A(V) approximate to 0.2 mag, combined with high column densities determined from the X-ray and optical spectroscopy (N-H > 10(21) cm(-2)), indicate a low dust-to-metals ratio and a possible overabundance of the light metals. An apparent small ratio of total to selective extinction (R-V approximate to 2) argues against dust destruction by the GRB. Time constancy of both the IR/optical/UV spectral energy distribution and the soft X-ray absorption suggests that the absorbing material is not local to the GRB.

An XMM-Newton observation of the east radio lobe of the nearby radio galaxy Fornax A is reported. The diffuse hard X-ray emission associated with the east lobe, which was initially discovered by ASCA and ROSAT, is confirmed with significant signal statistics, after strictly removing 59 sources detected within the MOS field of view. Its X-ray spectrum is described by a single power-law model, which is absorbed by a medium with a column density consistent with that toward the object. The best-fit X-ray photon index, Gamma(X) = 1.62(-0.15)(+0.24), agrees with the synchrotron radio index, Gamma(R) = 1.68 +/- 0.1, determined from the radio spectrum between 29.9 MHz and 5 GHz. Hence, the inverse Compton interpretation for the diffuse X-rays is justified. The X-ray flux density in the east lobe is measured to be 90 +/- 21 nJy at 1 keV (including both statistical and systematic errors) with the index fixed at the radio value. This gives electron and magnetic energy densities of 3.0(-1.0)(+1.5) x 10(-13) and 6.1(-3.5)(+5.7) x 10(-14) ergs cm(-3), respectively. The latter corresponds to a magnetic field strength of 1.24(-0.40)(+0.50) mu G, which is smaller than the field estimated under the minimum energy condition, 1.55 mu G, although with a slightly large error. Reevaluation is also made of the ASCA result on the west lobe, to show that both lobes share a similar physical condition in terms of energetics.

An XMM-Newton observation of the east radio lobe of the nearby radio galaxy Fornax A is reported. The diffuse hard X-ray emission associated with the east lobe, which was initially discovered by ASCA and ROSAT, is confirmed with significant signal statistics, after strictly removing 59 sources detected within the MOS field of view. Its X-ray spectrum is described by a single power-law model, which is absorbed by a medium with a column density consistent with that toward the object. The best-fit X-ray photon index, Gamma(X) = 1.62(-0.15)(+0.24), agrees with the synchrotron radio index, Gamma(R) = 1.68 +/- 0.1, determined from the radio spectrum between 29.9 MHz and 5 GHz. Hence, the inverse Compton interpretation for the diffuse X-rays is justified. The X-ray flux density in the east lobe is measured to be 90 +/- 21 nJy at 1 keV (including both statistical and systematic errors) with the index fixed at the radio value. This gives electron and magnetic energy densities of 3.0(-1.0)(+1.5) x 10(-13) and 6.1(-3.5)(+5.7) x 10(-14) ergs cm(-3), respectively. The latter corresponds to a magnetic field strength of 1.24(-0.40)(+0.50) mu G, which is smaller than the field estimated under the minimum energy condition, 1.55 mu G, although with a slightly large error. Reevaluation is also made of the ASCA result on the west lobe, to show that both lobes share a similar physical condition in terms of energetics.

NGC 1316 hosts the classical double lobe radio galaxy Fornax A. Recently, Kim and Fabbiano (2003) revealed with Chandra a 'blob' like emission associated with the optical dark lane, suggesting heating by the galaxy-merging. In this paper, we show a detail analysis focusing into the 'blob' to show significantly low temperature and low entropy. The significantly lower entropy in comparison with the other inter-stellar medium structures supports that the 'blob' are produced at the past galaxy merging. Comparing with those of non-thermal electrons in the radio lobes, we discuss a possible history of the nucleus activity and show its estimated kinetic luminosity during its active phase.

The hard X-ray detector (HXD-II) onboard Astro-E2 consists of a main detector with energy range 10-600 keV and a BGO active shield detector for background reduction. The shield detector wide-band all-sky monitor (WAM) has been designed not only for background reduction but also for all sky monitoring of gamma-ray bursts (GRB) and bright soft gamma-ray sources. WAM has a large geometrical structure of BGO scintillators for reinforcing its stopping power and has an asymmetric shape for reducing its weight. This particular structure of WAM makes the gamma-ray response very complicated, and thus we need careful calibrations before the launch. We then performed preflight calibrations of WAM as a part of the HXD-II calibrations in 2003-2004. We measured the pulse height spectra and stopping power of each unit counter individually before the HXD-II integration by exposing them to collimated gamma-rays. After integration of the HXD-II detector and installing it to the spacecraft, we measured the same issues as above for WAM by irradiating the gamma-ray source from various directions. Taking into account these experimental results, we constructed the gamma-ray response matrix of WAM using the Geant4 Monte Carlo simulation. The response developed in this work was found to have reproduced the experimental data within 10-20% accuracy.

The hard X-ray detector (HXD-II) is one of the three scientific instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled to be launched in 2005. This mission is very unique in a point of having a lower background than any other past missions in the 10-600 keV range. In the HXD-II, the large and thick BGO crystals are used as active shields for particle and gamma-ray background to the main detector. They have a wide field of view of similar to 2 pi and a large effective area of 400 cm(2) even at 1 MeV. Hence, the BGO shields have been developed as a wide-band all-sky monitor (WAM) with a broadband coverage of 50-5000 keV. In this paper, overall design and performance of the HXD-II/WAM based on the results of preflight calibration tests carried out in June 2004 are described. By irradiating various radio isotopes with the WAM flight model, we verified that it had comparable capabilities with other gamma-ray burst detectors.

The soft gamma-ray detector (SGD) onboard the Japanese future high energy astrophysics mission (NeXT) is a Compton telescope with narrow field of view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and cadmium telluride (CdTe) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10(-7) counts/s/cm(2) /keV; the silicon layers are required to improve the performance at a lower energy band (< 0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing it to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD: high quality CdTe, low noise front-end application-specific integrated circuit, and bump bonding technology. Energy resolutions of 1.7 keV (full-width at half-maximum) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.

The hard X-ray detector (HXD-II) onboard Astro-E2 consists of a main detector with energy range 10-600 keV and a BGO active shield detector for background reduction. The shield detector wide-band all-sky monitor (WAM) has been designed not only for background reduction but also for all sky monitoring of gamma-ray bursts (GRB) and bright soft gamma-ray sources. WAM has a large geometrical structure of BGO scintillators for reinforcing its stopping power and has an asymmetric shape for reducing its weight. This particular structure of WAM makes the gamma-ray response very complicated, and thus we need careful calibrations before the launch. We then performed preflight calibrations of WAM as a part of the HXD-II calibrations in 2003-2004. We measured the pulse height spectra and stopping power of each unit counter individually before the HXD-II integration by exposing them to collimated gamma-rays. After integration of the HXD-II detector and installing it to the spacecraft, we measured the same issues as above for WAM by irradiating the gamma-ray source from various directions. Taking into account these experimental results, we constructed the gamma-ray response matrix of WAM using the Geant4 Monte Carlo simulation. The response developed in this work was found to have reproduced the experimental data within 10-20% accuracy.

The hard X-ray detector (HXD-II) is one of the three scientific instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled to be launched in 2005. This mission is very unique in a point of having a lower background than any other past missions in the 10-600 keV range. In the HXD-II, the large and thick BGO crystals are used as active shields for particle and gamma-ray background to the main detector. They have a wide field of view of similar to 2 pi and a large effective area of 400 cm(2) even at 1 MeV. Hence, the BGO shields have been developed as a wide-band all-sky monitor (WAM) with a broadband coverage of 50-5000 keV. In this paper, overall design and performance of the HXD-II/WAM based on the results of preflight calibration tests carried out in June 2004 are described. By irradiating various radio isotopes with the WAM flight model, we verified that it had comparable capabilities with other gamma-ray burst detectors.

The soft gamma-ray detector (SGD) onboard the Japanese future high energy astrophysics mission (NeXT) is a Compton telescope with narrow field of view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and cadmium telluride (CdTe) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10(-7) counts/s/cm(2) /keV; the silicon layers are required to improve the performance at a lower energy band (< 0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing it to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD: high quality CdTe, low noise front-end application-specific integrated circuit, and bump bonding technology. Energy resolutions of 1.7 keV (full-width at half-maximum) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.

The XMM-Newton observation of the nearby FR II radio galaxy 3C 98 is reported. In two exposures on the target, faint diffuse X-ray emission associated with the radio lobes was significantly detected together with a bright X-ray active nucleus, of which the 2-10 keV intrinsic luminosity is (4-8) x 10(42) ergs s(-1). The EPIC spectra of the northern and southern lobes are reproduced by a single power-law model modified by the Galactic absorption, with a photon index of 2.2(-0.5)(+0.6) and 1.7(-0.6)(+0.7), respectively. These indices are consistent with that of the radio synchrotron spectrum, 1.73 +/- 0.01. The luminosities of the northern and southern lobes are measured to be 8.3(-2.6)(+3.3) x 10(40) and 9.2+(5.7)(-4.3) x 10(40) ergs s(-1), respectively, in the 0.7-7 keV range. The diffuse X-ray emission is interpreted as an inverse Compton emission, produced when the synchrotron-emitting energetic electrons in the lobes scatter off the cosmic microwave background photons. The magnetic field in the lobes is calculated to be about 1.7 mu G, which is about 2.5 times lower than the value estimated under the minimum energy condition. It is inferred that the energy density of the electrons exceeds that in the magnetic fields by a factor of 40-50.

Gamma-ray bursts (GRBs) come in two classes(1): long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift ( z approximate to 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars(2). In contrast, no short GRB had been accurately (< 1000) and rapidly ( minutes) located. Here we report the detection of the X-ray afterglow from - and the localization of - the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect(3,4) if the origin of this GRB is through the merger of neutron-star or blackhole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.

The XMM-Newton observation of the nearby FR II radio galaxy 3C 98 is reported. In two exposures on the target, faint diffuse X-ray emission associated with the radio lobes was significantly detected together with a bright X-ray active nucleus, of which the 2-10 keV intrinsic luminosity is (4-8) x 10(42) ergs s(-1). The EPIC spectra of the northern and southern lobes are reproduced by a single power-law model modified by the Galactic absorption, with a photon index of 2.2(-0.5)(+0.6) and 1.7(-0.6)(+0.7), respectively. These indices are consistent with that of the radio synchrotron spectrum, 1.73 +/- 0.01. The luminosities of the northern and southern lobes are measured to be 8.3(-2.6)(+3.3) x 10(40) and 9.2+(5.7)(-4.3) x 10(40) ergs s(-1), respectively, in the 0.7-7 keV range. The diffuse X-ray emission is interpreted as an inverse Compton emission, produced when the synchrotron-emitting energetic electrons in the lobes scatter off the cosmic microwave background photons. The magnetic field in the lobes is calculated to be about 1.7 mu G, which is about 2.5 times lower than the value estimated under the minimum energy condition. It is inferred that the energy density of the electrons exceeds that in the magnetic fields by a factor of 40-50.

Gamma-ray bursts (GRBs) come in two classes(1): long (> 2 s), soft-spectrum bursts and short, hard events. Most progress has been made on understanding the long GRBs, which are typically observed at high redshift ( z approximate to 1) and found in subluminous star-forming host galaxies. They are likely to be produced in core-collapse explosions of massive stars(2). In contrast, no short GRB had been accurately (< 1000) and rapidly ( minutes) located. Here we report the detection of the X-ray afterglow from - and the localization of - the short burst GRB 050509B. Its position on the sky is near a luminous, non-star-forming elliptical galaxy at a redshift of 0.225, which is the location one would expect(3,4) if the origin of this GRB is through the merger of neutron-star or blackhole binaries. The X-ray afterglow was weak and faded below the detection limit within a few hours; no optical afterglow was detected to stringent limits, explaining the past difficulty in localizing short GRBs.

The Burst Alert Telescope (BAT) onboard the Swift gamma-ray burst explorer has a coded aperture mask and a detector array of 32 K CdZnTe semiconductor devices. Due to the small mobility and short lifetime of carriers, the electron-hole pairs generated by gamma-ray irradiation cannot be fully collected. Hence the shape of the measured spectra has a broad low-energy tail. We have developed a method to model the spectral response by taking into account the charge transport properties which depend on the depth of the photon interaction [1]. The mobility-lifetime products for detectors derived from our method vary by more than one order of magnitude among detectors. In this paper, we focus on the nonuniformity of the mobility at the millimeter scale by employing a scanning experiment for a single detector. We reveal almost an order of magnitude variance in the mobility-lifetime product of holes within a single detector, while those of electrons, remains fairly uniform.

The Hard X-ray Detector (HXD-II) is one of the scientific payloads on board the fifth Japanese cosmic X-ray satellite Astro-E2, scheduled for launch in 2005. The HXD-II is designed to cover a wide energy range of 10-600 keV with a high sensitivity of about 10(-5) cnt/s/cm(2) /keV. In order to derive the energy response of the sensor and to estimate the background, a Monte Carlo simulator based on the Geant4 toolkit is currently being developed. This paper describes the design concept of the HXD-II software package, including the analysis tools and the Monte Carlo simulator, and its verification through a comparison with actual data taken by pre-flight radio-isotope irradiation experiments, together with calculated outputs that can demonstrate the in-orbit performance of the HXD-II.