Makoto Tashiro

ASTRO-E Hard X-ray Detector (HXD) is characterized by well-type phoswich counters in a compound-eye configuration which reduce the X-ray and non X-ray background to lower level than any other past hard X-ray missions. When operating in Low Earth Orbit, the expected background of the HXD is an order of 10-5[counts/s/keV/cm2], mainly caused from the radioactivity induced within the detector materials by nuclear interactions with geomagnetically trapped protons. Results are presented from measurements of induced radioactivity in two phoswich scintillators, GSO and BGO, irradiated by mono-energetic protons at an accelerator facility. Radiation transport computer codes are used to build the detector response functions against emissions from decays of spallation products. Based on the comparison of experimental and simulation results, the activation background level of HXD in the orbit is estimated.

We report the first results of the ground test of the Hard X-ray Detector (HXD) on board the Astro-E mission, by means of the newly developed Ground Support Equipment (GSE). Astro-E will be launched in 2000 by a Japanese M-V rocket. In order to verify the detector system during the limited time before launch, fast and versatile GSE is necessary. For this, we have developed a flexible test system based on nine VME I/O boards for a SUN workstation. These boards carry reconfigurable Field Programmable Gate Arrays (FPGAs) with 50,000 gates, together with 1 Mbyte SRAM devices tightly coupled to each FPGA device. As an application of using this GSE, we have tested the performance of a phoswich unit of the Flight Model of the HXD. In this paper, we present a schematic view of the GSE highlighting the functional design, and the results of our ground test of the HXD-sensor under the high count rate environment (approximately 10 kHz/unit) expected in orbit.

We present results of multiband analysis for 18 blazars observed with the X-ray satellite ASCA, half of which were also observed contemporaneously with EGRET instrument onboard Compton Gamma-ray Observatory (CGRO). Our multi-band analysis suggests that the magnetic field is 0.1 similar to 1 gauss. With these values of B, we estimate gamma(b) is 10(3) similar to 10(4) for quasar-hosted blazars (QHBs), and 10(5) for X-ray selected BL Lac objects (HBLs).

ASTRO-E is the fifth Japanese X-ray astronomy satellite scheduled to be launched in year 2000. The satellite will carry three scientific instruments, one of which is the Hard X-ray Detector (HXD). HXD will cover the 10-600 keV band with low background of several x 10(-6)c/s/cm(2)/keV. This will be achieved by the well-type phoswich counter technique together with large active shield counters of EGO (about 1200 cm(2)/side), which are also capable to detect GRBs in the 100-2000 keV band. About 100 GRBs are expected to be detected per year with HXD.

The fourth Japanese x-ray astronomy satellite, ASCA, carries two imaging gas scintillation proportional counters (GIS) on its focal plane. Extensive ground calibration has established its position resolution to be 0.5 mm and FWHM energy resolution to be 8.0% both at 6 keV. When combined with the x-ray telescope, a sensitivity range becomes 0.7 - 10 keV. These properties have been confirmed through in-orbit calibrations. The in-orbit background of the GIS has been confirmed to be as low as (5 - 7) × 10 -4 c s -1cm -2keV -1 over the 1 - 10 keV range. The long-term detector gain is stable within a few % for two years. Gain dependence on the position and temperature has been calibrated down to 1%. The overall energy response is calibrated very accurately. Thus the GIS is working as an all-round cosmic x-ray detector.