LXeGRIT - A Liquid Xenon Gamma-Ray Imaging Telescope

Columbia University
Rice University
University of New Hampshire
Waseda University , Japan


The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon-borne experiment which uses a liquid xenon time projection chamber (LXeTPC) to image gamma-ray emission from cosmic sources in the 0.15 -10 MeV energy band. The detector is the original prototype developed at Columbia to demonstrate gamma-ray spectroscopy and imaging in a homogeneous, 3D position sensitive LXeTPC with combined charge and light readout. To verify the application of this technology in space, the TPC was turned into a balloon-borne instrument, and tested in three flight campaigns, from the Northern Hemisphere. Following the first engineering flight, of short duration, in 1997, LXeGRIT was successfully operated as gamma-ray telescope on two longer duration flights in 1999 and 2000. A total of about 36 hours of data have been accumulated with the LXeTPC at an average altitude of 39 km. The background rate measured in flight is consistent with that expected from the dominant flux of atmospheric gamma-rays, confirming the radiation hardness of Xe as detector material. The gamma-ray data from the strongest source in the sky, the Crab Nebula/Pulsar, in the 1 steredian field-of-view of LXeGRIT for more than 10 hours, are being analyzed to verify the response as Compton imager and polarimeter. LXeGRIT is a collaboration between Columbia, the University of New Hampshire, Waseda University in Japan and Padova University in Italy. The LXeGRIT balloon flight program and the continuing R&D on xenon imaging detectors for future missions in high energy astrophysics is supported by NASA.