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J. E. Grindlay (Harvard-Smithsonian Center for Astrophysics)
We are carrying out a recently approved Concept Study for an Ultra-Long Duration Balloon (ULDB) mission to carry out the first high sensitivity and resolution imaging sky survey in the hard x-ray (20-600 keV) band. The Energetic X-ray Imaging Survey Telescope--Long Integration Time Experiment (EXIST-LITE) would survey ~1/2 the sky each day with an array of 4 large area (1600 cm2 each) and large field of view (40deg X 40deg, each) coded aperture telescopes. By orienting the combined 40deg X 80deg FOV North-South, sources are observed (drift scan) for ~3-12h/day and imaged for ~0.5-3arcmin source locations with 1mCrab sensitivity (30-200 keV) for the full 100d ULDB mission. With a single mid-latitude ULDB flight from both southern and northern launch sites, the EXIST-LITE survey would achieve sensitivities ~10-100X greater than any previous (HEAO-A4; all sky) or planned (INTEGRAL; imaging galactic plane survey) missions. It would enable key new studies of gamma-ray bursts, AGN, galaxy clusters, x-ray binaries, stars and possible hidden supernova remnants and be a pathfinder for followup pointed missions such as the focussing hard x-ray telescope (HXT) on Constellation-X. This talk will focus on some of the details of the science objectives and how they relate to current wide-field HX survey studies being conducted with BATSE and BeppoSAX (WFC) as well as recent HX results from narrow-field instruments (e.g. BeppoSAX/PDS). Our ongoing technology development for both the imaging HX detectors (employing Cd-Zn-Te pixellated arrays) and some of the ULDB gondola systems will also be described.