Preliminary results from the 1999 balloon flight of the Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT)

LXeGRIT is a balloon-borne Compton telescope employing a large volume liquid xenon time projection chamber (LXe-TPC) as the central (gamma) -ray detector. It is designed to image (gamma) - rays in the energy range of approximately 200 keV to 20 MeV, with an angular resolution of about 3 degrees (1 sigma) at 2 MeV, within a field-of-view (FOV) of about 1 sr. The detector's energy and three-dimensional spatial resolution as measured during pre-flight calibration experiments, are (Delta) E1xe/E equals 8.8% (root)1MeV/E and < 1 mm RMS, respectively. The detection efficiency for Compton events varies between 1.5% and 4% depending on energy and event selection. We describe the instrument as flown on May 7, 1999 and review its overall performance at balloon altitude. The launch occurred at 13:26:54 UT from Ft. Sumner, New Mexico and the flight was terminated about 9 hours later. The Crab was in the instrument FOV for a few hours. Analysis of these data is in progress.