HIGH-RESOLUTION GE SPECTROMETER FOR GAMMA-RAY BURST ASTRONOMY

The Transient Gamma-Ray Spectrometer (TGRS) to be flown aboard the WIN D spacecraft is primarily designed to perform high resolution spectros copy of transient gamma-ray events, such as cosmic gamma-ray bursts an d solar flares over the energy range 25 keV to 8.2 MeV with an expecte d spectroscopic resolution of similar to 3 keV at 1 MeV. The detector itself consists of a 215 cm(3) high purity n-type Ge crystal kept at c ryogenic temperatures by a passive radiative cooler. The geometric fie ld of view defined by the cooler is similar to 1.8 pi steradian. To av oid continuous triggers by soft solar events, a thin BeCu Sun-shield a round the sides of the cooler has been provided. A passive Mo/Pb occul ter, which modulates signals from within +/-5 degrees of the ecliptic plane at the spacecraft spin frequency, is used to identify and study solar flares, as well as emission from the galactic plane and center. Thus, in addition to transient event measurements, the instrument will allow the search for possible diffuse background lines and monitor th e 511 keV positron annihilation radiation from the galactic center. In order to handle the typically large burst count rates, which can be i n excess of 100 kHz, burst data are stored directly in an onboard 2.75 Mbit burst memory with an absolute timing accuracy of +/-1.5 ms after ground processing. The memory is capable of storing the entire spectr al data set of all but the largest bursts. WIND is scheduled to be lau nched on a Delta II launch vehicle from Cape Canaveral on November 1, 1994. After injection into a phasing orbit, the spacecraft will execut e a double lunar swing-by before being moved into a controlled 'halo' orbit about the L1 Lagrangian point (similar to 250 R(e) towards the S un). This will provide a 5 light-second light travel time with which t o triangulate gamma-ray burst sources with Earth-orbiting systems, suc h as those on-board the Gamma-Ray Observatory (GRO). The response of i nstrument to transient gamma-ray events such as GRB's and solar flares will be presented as well as the expected response to steady state po int sources and galactic center line emission.