Capability of the ASTRO-E Hard X-ray Detector
for High-Energy Transients and g-Ray Bursts
Y. Terada, K. Yamaoka, M. Kokubun, J. Kotoku, T. Mizuno, J. Kataoka, T. Takahasi, T. Murakami, K. Makishima, T. Kamae and the HXD team
The Hard X-Ray Detector(HXD) is one of the instruments
onboard the Japanese cosmic X-ray/g-ray satellite ASTRO-E,
scheduled for launch in January 2000.
The HXD covers the energy range from 10 keV to 700 keV
with a very low background,
typically 1 ×10-5 c s-1 cm-2 keV-1
at 200 keV on ground,
with a typical effective area of 330 cm2 at 50 keV.
The X-ray detection part consists
of 4×4 GSO/BGO well-type phoswitch scintillators
and 64 2mm silicon PIN diodes,
surrounded by 20 Anti-counters working as active shields on 4 sides.
The Anti-counters are made of 4 cm thick BGO crystals,
with a very large geometrical area 1200 cm2 per one side,
remaining the effective area 600 cm2 per one side at 1 MeV.
The Anti-counters are additionally used for monitoring
high-energy transient sources and g-ray bursts
in an energy range of 100 keV to 2 MeV.
The transient monitoring function is achieved by Earth Occulation method.
For an accurate position determination of transient objects,
X-ray spectra from the Anti-counters are read out every 1 sec
(0.5 sec on condition)
with an absolute timing accuracy of 30.5 m sec.
The onboard CPU compress these spectra data
when the telemetry limitation is severe.
The g-ray burst detection is achieved by monitoring
the Anti-counter counting rates with a time resolution of 1/32 sec.
The automated burst detection algorithm utilizes
both hardware circuits and the onboard software.
Once a g-ray burst occurs,
light curve data of Anti-counter before and after burst is telemetered.
The overall anglar responce of the Anti-counters has been measured
in laboratory by irradiating them with isotopes from various directions
in June 1999.
Based on this calibration information,
crude positions of the g-ray bursts can be determined
by comparing signal intensities detected on the four sides.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.