ar X iv : a st ro - p h / 97 12 35 9 v 1 1 J an 1 99 8 Proposed ( to ) EXIST : Hard X - ray Imaging All Sky Survey / Monitor

The hard x-ray (10-600 keV) sky is inherently time variable and yet has neither been surveyed nor been monitored with a sensitive imaging telescope. The Energetic X-ray Imaging Survey Telescope (EXIST) is a mission concept, proposed for MIDEX, which would conduct the first imaging all-sky hard x-ray survey as well as provide a sensitive all sky monitor (ASM). With ∼60% sky coverage each orbit, and full sky coverage each ∼50 days, hard x-ray studies of gamma-ray bursts, AGN, galactic transients, x-ray binaries and accretion-powered pulsars can be conducted over a wide range of timescales. We summarize the scientific objectives of EXIST for both the survey and monitoring objectives. We describe the mission concept and the instrumentation approach, which incorporates a large area array of Cd-Zn-Te (CZT) detectors, as well as some of our ongoing development of CZT array detectors.