The Swift Gamma-Ray Burst Explorer Burst Alert Telescope (BAT)

The Swift Gamma Ray Burst Explorer, to be launched in late September 2003, will observe hundreds of gamma ray bursts per year and study their X-ray and optical afterglow with its multiwavelength complement of three instruments: a large gamma ray telescope called the Burst Alert Telescope (BAT), an X-Ray Telescope (XRT), and a UV/Optical Telescope (UVOT). The BAT is a large coded aperture gamma ray telescope with a wide field-of-view that provides the gamma ray burst triggers for the Swift Mission. BAT will observe and locate hundreds of bursts per year to better than 4 arc minutes accuracy. Using this prompt burst location information, Swift will slew quickly (within 20-70 s) and autonomously to point the on-board narrow field-of-view XRT and UVOT instruments at the burst for continued afterglow studies. A full description of the BAT instrument, including its 32,768-element CdZnTe detector array are presented and performance results from initial tests of BAT detector modules are also discussed.