Burst alert telescope (BAT) instrument response generation

The Burst Alert Telescope (BAT) aboard the Swift Gamma-ray Burst Explorer, which is scheduled for launch in early 2004, is a coded aperture telescope that includes an array of 32,768 planar CZT detectors, each 4 mm × 4 mm × 2 mm thick. The mobility-lifetime products for holes and electrons are used to characterize the charge transport properties of each detector and were measured during pre-flight calibration tests in early 2003. These values were found to vary over an order of magnitude from detector to detector. A charge transport model involving overall effective mobility-lifetime products for the full array, along with other more empirical models, is used to characterize the various components of the response of the BAT array to 15 - 150 keV gamma radiation from any direction in BAT's field-of-view (FOV). The full angular and spectral response of the array as a whole can be parameterized and the spectral response of the instrument over the range of angles and energies can be generated in the form of an overall instrument response matrix. Here we present a preliminary instrument response model and discuss the spectral features it reproduces. The software to generate the response matrix for BAT is currently under development.