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G. Sato, K. Nakazawa, T. Takahashi, S. Watanabe (Institute of Space and Astronautical Science (ISAS), Japan), S. Barthelmy, J. Cummings, N. Gehrels, D. Hullinger, H. Krimm, C. Markwardt, A. Parsons, J. Tueller (NASA/Goddard Space Flight Center, USA), E. Fenimore, D. Palmer (Los Alamos National Laboratory, USA), Y. Okada, H. Takahashi (University of Tokyo, Japan), M. Suzuki, M. Tashiro (Saitama University, Japan)
The Burst Alert Telescope (BAT), a large coded aperture instrument with a wide field-of-view (FOV), provides the gamma-ray burst triggers and locations for the Swift Gamma-Ray Burst Explorer. The BAT detector plane consists of 32,768 individual CdZnTe semiconductor gamma-ray detectors (4 mm x 4 mm x 2 mm) read out by XA1 ASICs and arranged in an array 1 meter below the 2.6 m2 coded aperture mask. The detector response to incident 15 to ~150 keV photons must be measured for each individual detector to separate mask modulation effects from differences in detector efficiencies. The characteristics of the detectors alone are determined from the exposure of each "block" subarray (2048 detectors, = 32K/16 blocks) to gamma-rays from calibrated radioactive sources at many incident angles. One of the most important characteristics of CdZnTe itself is the low mobility-lifetime (\mu\tau) product of carriers in CdZnTe detectors, which produces a position dependency in the charge induction efficiency. Histogrammed spectral data from each block subarray are fitted to an analytic spectral model which takes the induction efficiency and interaction positions of photons into account. Since the model is parameterized by \mu\tau products, it can extract \mu\tau products for the 2048 individual detectors in each block. BAT detector response matrices must be constructed from parameters such as these \mu\tau products. When BAT is fully assembled, we will systematically measure its response to different radioactive sources positioned at numerous locations covering the entire field-of-view. The initial results from the BAT block calibrations will be discussed and the CdZnTe properties of the BAT detectors will be presented.
The author(s) of this abstract have provided an email address for comments about the abstract: gsato@astro.isas.ac.jp
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.