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The Hard X-ray Detector (HXD-II) is one of the three instruments onboard the Astro-E2 satellite scheduled for launch in 2005. The HXD-II consists of 16 main counters (Well units), surrounded by 20 active shield counters (Anti units). The Anti units have a large geometrical area of similar to 800 cm(2) with an uncollimated field of view covering similar to 2 pi steradian. Utilizing 2.6 cm thick BGO crystals: they realize a large effective area of 400 cm(2) for 1 MeV photons. In the energy range of 300-5000 keV, the expected effective area is significantly larger than those of other gamma-ray burst instruments, such as CGRO/BATSE, HETE-2/FREGATE, and GLAST/GBM. Therefore. the Anti units act as a Wideband All-sky, Monitor (WAM) for gamma-ray bursts in the energy range of 50-5000 keV.

We evaluated the radiation tolerance of three types of metal-can MOS Field Effect Transistors (FETs). They are candidates for flight electronics of the Hard X-ray Detector (HXD-II) experiment which is onboard the cosmic X-ray satellite Astro-E2 scheduled for launch in 2005. We irradiated FETs with a Co-60 gamma-ray source under several different experimental conditions, and measured changes in their I-V characteristic curves. After a 10 krad irradiation during which the gate voltage is set at 0 V, all types showed a decrease in the switching voltage by similar to 0.2-0.4 V. In addition, the gate conductance increased under some irradiation conditions. These experimental results may be explained in terms of trapped charges and boundary levels in the oxide layer beneath the gate electrode. We have confirmed that at least two types of FETs can be used in our satellite-borne experiment, one as relay-driving FETs and the other in TTL-ECL conversion circuits. (c) 2005 Published by Elsevier B.V.

An analysis was made of 0.3-15 keV X-ray spectra of a Narrow-Line Seyfert 1 Galaxy, Ton S180, using archival data from ASCA, RXTE, and XMM-Newton. At energies above 2.5 keV, a power-law with a photon index of similar to 2.3 successfully and consistently reproduced the spectra from all of these observatories. Assuming this power-law component to extend toward lower energies, a soft excess, which is one of the most remarkable features of Narrow-Line Seyfert 1 Galaxies, is explained by another power-law multiplied by a thermal cutoff at similar to 0.4 keV. Some similarities have been observed between this object and Galactic black hole binaries in very high state, the latter being realized under high accretion rates. Attempts have been made to interpret the soft excess in terms of Comptonization of the disk photons by an electron cloud surrounding the accretion disk, like BHBs in a very high state.

Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and gamma-ray detection. The high-atomic number of the materials (Z(Cd) = 48, Z(Te) = 52) gives a high quantum efficiency in comparison with Si. The large band-gap energy (E-g = 1.5 eV) allows to operate the detector at room temperature. Based on recent achievements in high-resolution CdTe detectors, in the technology of ASICs and in bump-bonding, we have proposed the novel hard X-ray and gamma-ray detectors for the NeXT mission in Japan. The high-energy response of the super mirror onboard NeXT will enable us to perform the first sensitive imaging observations up to 80keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixellated CdTe detector, will provide spectra and images in the wide energy range from 0.5 to 80keV. In the soft gamma-ray band up to similar to 1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several x 10(-8) photons(-1) keV(-1) cm(-1) in the hard X-ray region and a few X 10(-7) photons(-1) keV(-1) cm(-2) in the soft gamma-ray region. (c) 2005 Elsevier B.V. All rights reserved.

The temperature dependence (from -20 to +20 degrees C) of gamma-ray irradiated light outputs, energy resolutions, and decay time profiles of three YAG:Ce poly-ceramic scintillators is studied. The Ce concentrations are 0.5, 0.05, and 0.005 mol%. The relative light yield of the YAG:Ce with 0.5 mol% was measured as 1 : 1.08 : 1.14 at +20, 0, and -20 degrees C, respectively, including the temperature dependence of the photo-tube (-0.2%/degree). The energy resolution stays almost constant at 7.2% for 662 keV gamma-rays. The ceramic with 0.05 mol% shows the almost same properties, while the light yield of that with 0.005 mol% is 2-4 times lower (hence the energy resolution becomes 14-19%). All the scintillators exhibit good linearities within similar to 1% between the light output and the irradiated gamma-ray energy from 59.5 keV to 662 keV. The decay time constants of the dominant decay components are about 80 ns and 300 ns at +20 degrees C. As the temperature increases, the effective decay of all the ceramics becomes faster, because the decay time constants become shorter and the fractions of the faster components increase. This decrease of the slower components is thought to suppress the light yield toward higher temperatures. These results indicate that thermal quenching dominates the temperature dependence of the ceramic YAG:Ce, and that the effect is almost negligible below the room temperature for the ceramics doped with Ce by greater than or similar to 0.05 mo1%. Because of self absorption of Ce emission, the 0.5 mol% scintillator starts to show a slight decrease in its light yield at lower temperatures than the 0.05 mol% one.

As the detection part of an improved Fourier Synthesis imager, we developed a new one-dimensional γ-ray position sensor consisting of inorganic scintillators whose lights are read out by a silicon strip detector (SSD). The employed SSD has no metal anode, with its Al-cathode divided into 32 channels of 400 μm pitch. Electrodes of all channels are Albonded to a low noise analog ASIC, so that signals can be read out from all channels simultaneously. We fabricated a "stacked CsI scintillator", consisting of 20 CsI(Tl) scintillator plates each having a dimension of 10 mm × 10 mm × 0.3 mm, and 0.07 mm-thick light reflective sheets inserted between adjacent CsI plates. Coupling the scintillator and the SSD, γ-ray with energies ≳ 500 keV were successfully detected, with a position resolution of ∼0.37 mm. © 2005 IEEE.

The temperature dependence (from -20 to +20 degrees C) of gamma-ray irradiated light outputs, energy resolutions, and decay time profiles of three YAG:Ce poly-ceramic scintillators is studied. The Ce concentrations are 0.5, 0.05, and 0.005 mol%. The relative light yield of the YAG:Ce with 0.5 mol% was measured as 1 : 1.08 : 1.14 at +20, 0, and -20 degrees C, respectively, including the temperature dependence of the phototube (-0.2%/degree). The energy resolution stays almost constant at 7.2% for 662 keV gamma-rays. The ceramic with 0.05 mol% shows the almost same properties, while the light yield of that with 0.005 mol% is 2-4 times lower (hence the energy resolution becomes 14-19%). All the scintillators exhibit good linearities within ∼1 % between the light output and the irradiated gamma-ray energy from 59.5 keV to 662 keV. The decay time constants of the dominant decay components are about 80 ns and 300 ns at +20 degrees C. As the temperature increases, the effective decay of all the ceramics becomes faster, because the decay time constants become shorter and the fractions of the faster components increase. This decrease of the slower components is thought to suppress the light yield toward higher temperatures. These results indicate that thermal quenching dominates the temperature dependence of the ceramic YAG:Ce, and that the effect is almost negligible below the room temperature for the ceramics doped with Ce by ≳ 0.05 mol%. Because of self absorption of Ce emission, the 0.5 mol% scintillator starts to show a slight decrease in its light yield at lower temperatures than the 0.05 mol% one. © 2005 IEEE.

Archival XMM-Newton data of the central region of M31 were analyzed for diffuse X-ray emission. Point sources with 0.5-10 keV luminosity exceeding similar to4 x 10(35) ergs s(-1) were detected. Their summed spectra are reproduced well by a combination of a disk blackbody component and a blackbody component, implying that the emission mainly comes from an assembly of luminous low-mass X-ray binaries. After excluding these point sources, spectra were accumulated over a circular region of 6' (1.2 kpc) centered on the nucleus. In the energy range above 2 keV, these residual spectra are understood to mainly be contributions from unresolved faint sources and spillover of photons from the excluded point sources. There is in addition a hint of similar to6.6 keV line emission, which can be produced by a hot ( temperature of several keV), thin, thermal plasma. Below 2 keV the spectra involve three additional softer components expressed by thin thermal plasma emission models, for which the temperatures are similar to0.6, similar to0.3, and similar to0.1 keV. Their 0.5-10 keV luminosities within 6' are measured to be similar to1.2 x 10(38), similar to1.6; 10(38), and similar to4 x 10(37) ergs s(-1) in order of decreasing temperature. The archival Chandra data of the central region of M31 yielded consistent results. By incorporating different annular regions, all three softer thermal components were confirmed to be significantly extended. These results are compared with reports from previous studies. A discussion is presented on the origin of each thermal emission component.

We summarize significant improvements which have been achived in the development of Astro-E2 Hard X-ray Detector (HXD-II). An expanded energy range and better energy resolution have been achieved from progresses in device materials and redesigning of the front-end electronics. An improved estimation for the detector background in orbit has also been conducted based upon results from our proton irradiation experiment. The sensitivity of HXD-II can be expected to reach an order of 10(-6) [c s(-1) keV(-1) cm(-2)].

Using archival Chandra ACIS-S data, 0.5-8.OkeV X-ray spectra of two luminous X-ray sources in the nearby dwarf irregular galaxy NGC 4449 were studied. One, with an extremely high luminosity of 1.3 x 10(39) erg s(-1) in the 0.5-8.0 keV band, shows a spectrum that is well described with a power-law model of photon index similar to 2. Its properties are consistent with those of ultraluminous compact X-ray sources observed in nearby galaxies. The spectrum of the other, with a luminosity of 2.7 x 10(38) erg s(-1) in the same band, is successfully represented with a so-called multi-color disk blackbody emission model with an inner-most disk temperature of similar to 0.59keV. Its spectral parameters are typical of ordinary black hole binaries observed in our Galaxy and the Large Magellanic Cloud. These young population objects, together with a bright supernova remnant and diffuse hot gas already reported, suggest that the X-ray emission from irregular galaxies is generally enhanced by their recent star-forming activities.

The NeXT mission has been proposed to study high-energy non-thermal phenomena in the universe. The high-energy response of the super mirror will enable us to perform the first sensitive imaging observations up to 80 keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixelated CdTe detector, will provide spectra and images in the wide energy range from 0.5 keV to 80 keV. In the soft gamma-ray band upto similar to 1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several x 10(-8) photonsns/keV/cm(2) in the hard X-ray region and a few x 10(-7) photons/s/keV/cm(2) in the soft gamma-ray region.

Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe. CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and back-round rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors. In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD). We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.

The Hard X-ray Detector (HXD-II), one of instruments onboard the Astro-E2 satellite to be launched in February 2005, is in the final stage of its development. The HXD-II probes the universe in the energy range of 10-600 keV with a sensitivity by an order of magnitude better than those of previous missions. The assembly of the HXD-II completed in January 2004, followed by a series of pre-launch qualification tests. As a result, the design goals of the HXD-II have been met. These include; a background level of 5x10(-6) counts/s/keV/cm(2) at 200 keV for GSO and 1x10(-5) counts/s/keV/cm(2) at 30 keV for PIN; energy resolutions of 2.9 keV (PIN diode, at 59.5 keV) and 10% (GSO scintillator, at 662 keV); and low energy thresholds of 10 keV for PIN diodes and 30 keV for GSO scintillators. The measured background predicts a continuum sensitivity of a few x10(-6) photons/s/keV/cm(2). Anti-Counter units surrounding the HXD-II provide 50 keV-5 MeV information on gamma-ray bursts and bright X-ray transients.

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 similar to 10(-5) cnt/S/cm(2)/keV, using 16 identical GSO and BGO phoswich counters combined with 2 mm-thick silicon PIN diodes. In order to investigate the in-orbit performance of HXD-II in cosmic radiation environment, a Monte Carlo simulator based (in the Geant4 toolkit is currently developed. There are two main goals of this simulator, which is directly connected to the detector's performance. One is to derive energy response to photons within the acceptance energy range, with 5% accuracy, after several types of standard event-selection of the HXD-II. The other is to estimate detector background with 10% accuracy. In addition to the background caused directly by the primary and secondary cosmic-rays, of particular importance is the radio-activation background induced by MeV protons trapped in the South Atlantic Anomaly. The simulator is also used in the pre-launch verifications of the HXD-II hardware. This paper describes the design concept of the Monte Carlo simulator, and its verification through comparison with the actual data of pre-flight radio-isotope irradiation experiments, together with calculated outputs that can demonstrate the in-orbit performance of the HXD-II.

The Hard X-ray Detector (HXD-II) onboard Astro-E2 consists of the main detector which has its energy range from 10 to 600 keV and the active shield detector for background reduction. This shield detector (Anti detector) is designed to not only for the background reduction but also for the soft gamma-ray all sky monitor of Gamma-ray bursts (GRB) and black hole binaries. The asymetric shape and large size of BGO scintillators for the Anti counter make the gamma-ray response very complicated, and thus we need the careful calibration before the launch. We then performed preflight calibrations of HXD-II in 2003-2004. For the Anti detector, we measured the pulse height spectra and stopping power of the unit detector before integration by exposing it to the collimated gamma-ray. After integration of HXD-II, we measured the pulse height spectra and stopping power of the Anti detector by irradiating the gamma-ray source from various direction. Furthermore, we performed the same measurement after placing the HXD-II detector on the Astro-E2 spacecraft. Taking into account these experimental results, we construct the gamma-ray response by the Geant4 Monte Carlo simulation. The response developed in this work was found to reproduce the experimental spectra and the count distributions of each unit counter with 10-20 % accuracy.

Employing Fourier-synthesis optics and one-dimensional position-sensitive detectors, we are developing a novel hard X-ray imager which can work in the similar to 10 keV to similar to 200 keV range either as a telescope or a microscope. As the detection part of our imager, we have developed a strip detector made of Schottky CdTe diode, with its cathode divided into 64 channels of 150 mu m pitch. Electrodes of all channels are gold-stud bonded to a fanout board, and connected to low noise analog ASIC. We read out signals from all channels simultaneously. As the grid optics elements, one-dimensional modulation collimator grids of 1 mm thick tungsten have been manufactured, with 10 grid pitches ranging from 0.2 mm to 2 nun with harmonic ratios. Combining the CdTe strip detector and the modulation collimators, we have verified hard X-ray imaging performance of this system. Specifically, by observing an Am-241 source, we have successfully obtained an image in the 10-70 keV range.

The Hard X-ray Detector (HXD) is one of the three instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled for launch in 2005. This mission is very unique in a point of having a lower detector background than any other past missions in the 10-600 keV range. In the HXD, the large and thick BGO crystal are used as active shields for reducing the particle and gamma-ray background to the main detector. These anticoincidence shields are called as "Anti counters", which have a large geometrical area similar to 800 cm(2) and an uncollimated field of view of similar to 2 pi. Furthemore, they also have a larger effective area, corresponding to 400 cm(2) at even 1 MeV due to their thick high-Z materials. This feature enables us to observe the high energy radiation of Gamma-ray bursts with a higher sensitivity than previous all-sky monitors. Hence, the Anti counters have been developed as all-sky monitors with a broadband coverage of 50-5000 keV. In this paper, we will describe overall design of the HXD Anti counters, then report on the results of the pre-flight calibration test on June 2004 using the flight model. By irradiating various radio isotopes with Anti counters, we confirmed that they have capability as all-sky monitors. It is striking that the low energy threshold has been archived about 30 keV in spite of large volume of BGO scintillators.

The Soft Gamma-ray Detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), 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 CdTe (Cadmium Telluride) detectors. It can detect photons in a wide energy hand (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 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 ASIC and bump bonding technology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of MC simulation used to evaluate the performance of the SGD.

We measured basic properties of three ceramic Y3Al5O12 (YAG) scintillators doped with Ce to a concentration of 0.5, 0.05, and 0.005 mol%, in comparison with a single YAG scintillator unknown amount of Ce doping. First, transparency and emission spectrum were investigated. We confirmed that the transparency of the ceramics is compareble to that of the single one (similar to 80%) in wavelengths in longer than similar to 500 nm. The ceramics did not show an indication of lattice defects which is present in the single YAG. Then the response to gamma-rays was studied using a phototube as a scintillation light detector. The 0.5 mol% exhibited thehighest light yield (similar to 40% of CA), with an energy resolution of about 7.2% at Cs-137 662 keV photoabsorption peak. The optimum Ce Concentration for a similar to 2mm thick ceramic YAG was determined to be similar to 0.1 mol%. Using the delayed coincidence method, the principal time constant of the ceramic YAGs was measured as similar to 80 ns. By irradiating 5.49 MeV alpha-particles, the alpha-ray to gamma-ray light yield ratio of the ceramic YAGs was found to depend negatively on the amount of Ce.; namely, 0.28, 0.20, and 0.13 in the decreasing order of the concentration. The 200-1000 keV intrinsic background of the 0.5 mol% ceramic was similar to 10(-5) counts/s/cm(3), indicating that it is not significantly contaminated by radioactive impurities.

We present an INTEGRAL observation of the Cen-Crux region in order to search the electron cyclotron resonance scattering features from the X-ray binary pulsars. During the AO1 200 ks observation, we clearly detected 4 bright X-ray binaries, 1 Seyfert Galaxy, and 4 new sources in the Field of view. Especially from GX301-2, the cyclotron resonance feature is detected at about similar to 37 keV, and width of 3-4 keV. In addition, the depth of the resonance feature strongly depends on the X-ray luminoscity. This is the first detection of luminosity dependence of the resonance depth. The well-known twin pulsars are spatially separated by JEM-X and IBIS/ISGRI, and pulse periods are measured individually; 296.90 sec for 1E1145-6141 and 292.5 sec for 4U1145-619. The cyclotron resonance feature is marginally detected from 1E1145.1-6141. Cen X-3 was very dim during, the observation and poor statistics disable its to detect the resonance features.

The Soft Gamma-ray Detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), 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 CdTe (Cadmium Telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 × 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 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 ASIC and bump bonding tecnology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of MC simulation used to evaluate the performance of the SGD. © 2004 IEEE.

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 ∼ 10-5 cnt/s/cm2/keV, using 16 identical GSO and BGO phoswich counters combined with 2 mm-thick silicon PIN diodes. In order to investigate the in-orbit performance of HXD-II in cosmic radiation environment, a Monte Carlo simulator based on the Geant4 toolkit is currently developed. There are two main goals of this simulator, which is directly connected to the detector's performance. One is to derive energy response to photons within the acceptance energy range, with 5% accuracy, after several types of standard event-selection of the HXD-II. The other is to estimate detector background with 10% accuracy. In addition to the background caused directly by the primary and secondary cosmic-rays, of particular importance is the radio-activation background induced by MeV protons trapped in the South Atlantic Anomaly. The simulator is also used in the pre-launch verifications of the HXD-II hardware. This paper describes the design concept of the Monte Carlo simulator, and its verification through comparison with the actual data of pre-flight radio-isotope irradiation experiments, together with calculated outputs that can demonstrate the in-orbit performance of the HXD-II. © 2004 IEEE.

The Hard X-ray Detector (HXD) is one of the three instruments onboard Japanese X-ray astronomy satellite Astro-E2 scheduled for launch in 2005. This mission is very unique in a point of having a lower detector background than any other past missions in the 10-600 keV range. In the HXD, the large and thick BGO crystal are used as active shields for reducing the particle and gamma-ray background to the main detector. These anticoincidence shields are called as "Anti counters", which have a large geometrical area ∼ 800 cm 2 and an uncollimated field of view of ∼ 2π. Furthemore, they also have a larger effective area, corresponding to 400 cm2 at even 1 MeV due to their thick high-Z materials. This feature enables us to observe the high energy radiation of Gamma-ray bursts with a higher sensitivity than previous all-sky monitors. Hence, the Anti counters have been developed as all-sky monitors with a broadband coverage of 50-5000 keV. In this paper, we will describe overall design of the HXD Anti counters, then report on the results of the pre-flight calibration test on June 2004 using the flight model. By irradiating various radio isotopes with Anti counters, we confirmed that they have capability as all-sky monitors. It is striking that the low energy threshold has been archived about 30 keV in spite of large volume of BGO scintillators. © 2004 IEEE.

Cadmium Telluride (CdTe), with its high photon absorption efficiency, has been regarded as a promising semiconductor material for the next generation X/gamma-ray detectors. In order to apply this device to astrophysics, it is essential to investigate the radiation hardness and background properties induced by cosmic-ray protons in orbit. We irradiated Schottky CdTe diodes and a CdTe block with a beam of mono-energetic (150 MeV) protons. The induced activation in CdTe was measured externally with a germanium detector, and internally with the irradiated CdTe diode itself. We successfully identified most of radioactive isotopes induced mainly via (p, xn) reactions, and confirmed that the activation background level of CdTe diode is sufficiently low in orbit. We compared energy resolution and leakage current before and after the irradiation and also monitored the signals from a calibration source during the irradiation. There have been no significant degradation. CdTe diodes are tolerant enough to radioactivity in low earth orbit.

With its high stopping power, Cadmium Telluride (CdTe) has been regarded as a promising semiconductor material for the next generation X/gamma-ray detectors, and improved significantly during this decade. In order to apply this device to astrophysics, it is essential to investigate the radiation hardness and background properties induced by cosmic-ray protons. We irradiated Schottky CdTe diodes and a CdTe block with a beam of mono-energetic (150 MeV) protons. The induced radio-activation in CdTe was measured externally with a germanium detector, and internally with the irradiated CdTe diode itself. We successfully identified most of radioactive isotopes induced mainly via (p, xn) reactions, and confirmed that activation background level of the CdTe diode is sufficiently low in orbit. We compared energy resolution and leakage current before and after the irradiation, and also monitored the signals from a calibration source during the irradiation. There have been no significant degradation. CdTe diodes are enough tolerant to radioactivity in orbit.

Cerium-doped gadolinium silicic dioxide crystal, GSO(Ce), is a high-Z that gives higher light yield than BGO, and can potentially replace NaI(Tl), CsI(Tl) and BGO in many applications, Its production cost, however, has been substantially higher than any of them, while its energy resolution has been worse than that of NaI(Tl) or CsI(Tl). The merit did not overcome these deficiencies except in limited applications. We developed a low background phoswich counter (the well-type phoswich Counter) for the Hard X-ray Detector of the Astro-E project based on GSO scintillator. In the developmental work, we have succeeded in improving the light yield of GSO(Ce) by 40-50%. For energies above 500 keV, a large GSO(Ce) crystal (4.5 cm (.) 4.5phi cm) now gives energy resolution comparable to or better than the best NaI(Tl) when read out with a phototube. With a small GSO(Ce) crystal (5 x 5 x 5 mm(3)) and a photodiode, an energy resolution comparable to or better than the best CsI(Tl) has been obtained. With this improved performance, we find that the much higher photopeak efficiency and the shorter scintillation decay time of GSO(Ce) offsets its higher cost for many applications. We summarize our past developmental work to decrease radioactive contamination and to increase light yield of GSO(Ce) for astronomical hard X-ray detection. Included also are measurements done after the unsuccessful launch of the Astro-E mission. The work is still continuing for the remake version of Astro-E Hard X-ray Detector. (C) 2002 Elsevier Science B.V. All rights reserved.

This paper summarizes the design and performance of the hard X-ray detector constructed for the ASTRO-E satellite. The detector utilizes the GSO/BGO well-type phoswich counters in a compound-eye configuration to achieve an extremely low background level of a few x 10(-5) counts s(-1) cm(-2)keV(-1) [1]. The GSO scintillators installed in the BGO active shield wells are sensitive to 30-600 keV photons, while the 2-mm-thick silicon PIN diodes, placed in front of each GSO crystal, cover the 10-60 keV energy band with a spectral resolution of similar to3.5-keV full-width at half-maximum. The design goals, of both low background and high energy resolution, in the hard X-ray bands were verified through the preflight calibration experiments.

A multi-Compton gamma-ray telescope based on high resolution semiconductor materials (Semiconductor Multi-Compton Telescope (SMCT) or Advanced Compton Telescope (ACT)) is a promising approach to achieve high sensitivity for gamma-rays with energies from several hundred keV up to several MeV. A SMCT utilizing several tens of layers of thin CdTe (Cadmium Telluride) detector is an attractive concept to obtain higher detection efficiency in comparison with Si-based SMCT. Recently we have developed high energy-resolution CdTe diode detectors. A large-area detector with dimensions of 2.15 × 2.15 cm2 with a thickness of 0.5 mm shows an energy resolution of better than 3 keV (FWHM) at 60 keV. In order to extend the application of CdTe diodes to the detection of MeV gamma-rays, we have constructed a stacked detector consisting of 40 layers of large CdTe diodes. Here we report the recent progress on the high-resolution CdTe diode and describe the conceptual design of new Multi-Compton Gamma-ray telescopes based on Monte Carlo simulation. An idea of active pair production telescope is briefly described.

The ASTRO-E Hard X-ray Detector utilized GSO/BGO well-type phoswich counters in compound-eye configuration [1], to achieve an extremely low background level of a few x 10(-5)counts s(-1) cm(-2) keV(-1). The GSO scintillators installed in the BGO active shield wells observes 30-600 keV photons, while silicon PIN diodes of 2 mm thick placed in front of each GSO crystal covers 10 - 60 keV photons with energy resolution of similar to3.5 keV FWHM. The design goals both of low background and high energy resolution in the hard X-ray bands were confirmed to be achieved through the preflight calibration experiments.

Using ASCA, spatially integrated X-ray spectra of the central regions of M 31 were studied. Data were accumulated over three different circular regions, with radii of 3', 6', and 12', all centered on the nucleus. The spectra are relatively similar among the three regions. In the energy range above 1.5 keV, the spectra are reproduced by a combination of a disk black-body component and a black-body component, implying that the emission mainly comes from an assembly of low-mass X-ray binaries. At energies below 1.5 keV, the spectra involve two additional softer components, expressed by thin-thermal plasma emission models of temperatures of similar to 0.9 keV and similar to 0.3 keV. Over the central 12' (2.4 kpc) region and in the 0.5-10 keV energy band, the binary component has a luminosity of 2.6 x 10(39) erg s(-1), while the two softer components both exhibit luminosities of similar to 2 x 10(38) erg s(-1). These results are compared with those from other missions, including Chandra and XMM-Newton in particular. A discussion is presented on the nature of the two softer spectral components besides the binary one.

The ASTRO-E hard X-ray defector utilizes GSO(Gd2SiO5:Ce 0.5% mol)-BGO(Bi4Ge3O12) well-type phoswich counters [1] in compound-eye configuration to achieve an extremely low background level of about a few times 10(-5) counts s(-1) cm(-2) keV(-1). The GSO scintillators placed at the bottom of the BGO well observe photons in the energy range 30-600 keV. To cover the lower energy range of 10-60 keV, silicon p-i-n diodes of 2 mm in thickness and 21.5 x 21.5 mm(2) in size were newly developed and placed in front of the GSO scintillators. The p-i-n diode exhibits complex spectral responses, including subpeak and low energy tail components. To examine the origin of these components, we measured the spatially resolved response of the p-i-n diode and confirmed that the subpeak and the low energy tall are related to the electrode structures. and electric, fields in the p-i-n. diode, respectively.

A brief description is made of the HXD-II instrument, which is to be onboard the Astro-E2 mission to substitute the HXD (Hard X-ray Detector) instrument onboard the lost Astro-E.

The bulge X-ray emission has been systematically studied with the ASCA and RXTE satellites. After removing the contribution from point sources, the presence of diffuse bulge X-ray emission consisting three distinct emission components, two thermal (cooler and hotter) and one non-thermal, has been established. The temperatures of the thermal components are essentially constant (0.6 keV and 3 keV) all over the bulge region, and surface brightness distributions of the hotter and non-thermal components are strongly correlated with each other. From the estimated scale of the hard X-ray bulge, total X-ray luminosity of the bulge emission is estimated to be similar to 10(38) erg s(-1), which is almost comparable to that of the well-known GRXE.

The Hard X-Ray Detector (HXD) is one of the instruments on board ASTRO-E, scheduled for lanch in January-February 2000. The HXD consists of 16 Well-type phoswich counters, surrounded by 20 active shield counters (Anti Coincidence Counters: Anti-Counters). It covers the energy range 10-600 keV with a very low background. Because the Anti-Counters are made of thich high-Z material with a very large geometrical area, they retain a large effective area up to high energies. Therefore the Anti-Counters can be used for monitoring high-energy transient sources and gamma-ray bursts. In this paper, the ail sky monitoring function with the Anti-Counters and the result of their ground calibration tests are described.

Thick and large area PIN diodes for the hard X-ray astronomy in the 10-60 keV range are developed. To cover this energy range in a room temperature and in a low background environment, Si PIN junction diodes of 2 mm in thickness with 2.5 cm(2) in effective area were developed, and will be used in the bottom of the Phoswich Hard X-ray Detector (HXD), on-board the ASTRO-E satellite. Problems related to a high purity Si and a thick depletion layer during our development and performance of the PIN diodes are presented in detail. (C) 1999 Elsevier Science B.V. All rights reserved.

The Bard X-ray Detector (HXD) is one of the three instruments on the fifth Japanese cosmic X-ray satellite ASTROE , scheduled for launch in January, 2000. The HXD covers a wide energy range of 10-600 keV, using 16 identical GSO/BGO phoswich-counter modules, of which the low-energy efficiency is greatly improved by adding 2 mm-thick silicon PIN diodes. Production of the HXD between completed and pre-flight calibration is now in progress. The design concept of the HXD sensor, detail of the production process, and a brief summary of the measured performance is reported.

ASTRO-E is the next Japanese X-ray satellite to be launched in the year of 2000, It carries three high-energy astrophysical experiments, including the Hard X-ray Detector (HXD) which is unique in covering the wide energy band from 10 keV to 700 keV with an extremely low background. The HSD is a compound-eye detector, employing 16 GSO/BGO well-type phoswich scintillation counters together with 64 silicon PIN detectors. The scintillation counters cover an energy range of 40-700 keV, while the PIN diodes fill the intermediate energy range from 10 keV to 70 keV with an energy resolution about 3 keV. In this paper, we report on the developments of the large area, thick silicon PIN diodes. In order to achieve a high quantum efficiency up to 70 keV with a high energy resolution, we utilize a double stack of silicon PIN diodes, each 20 x 20 mm(2) in size and 2 mm thick. Signals from the two diodes are summed into a single output. Four of these stacks (or eight diodes) are placed inside the deep EGO active-shield well of a phoswich counter, to achieve an extremely low background environment. Thus, the HXD utilizes 64 stacked silicon PIN detectors, achieving a total geometrical collecting area of 256 cm(2) We have developed the 2 mm thick silicon PIN diodes which have a low leakage current, a low capacitance, and a high breakdown voltage to meet the requirements of our goal. Through various trials in fabricating PIN diodes with different structures, we have found optimal design parameters, such as mask design of the surface p(+) layer and the implantation process.