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J. Grindlay (CfA), EXIST Science Working Group
The hard x-ray (HX) band (~5 - 600 keV) is one of the final astronomical frontiers without a full-sky imaging sensitive survey. The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed very large area coded aperture telescope array, incorporating ~8m2 of pixellated Cd-Zn-Te detectors, that would be mounted on the International Space Station to conduct a full sky imaging survey each 90min orbit. With a sensitivity (5\sigma, 1yr) of ~0.05mCrab (5-100 keV), it would extend the ROSAT (and possible ABRIXAS) soft/medium x-ray surveys into the HX band and enable identification and study of sources ~0\times fainter than with Swift. At ~100 - 600 keV, the ~1mCrab sensitivity is \ga100\times that achieved in the only previous (HEAO-A3; non-imaging) all-sky survey. EXIST would address a broad range of key science objectives: from obscured AGN, and the accretion luminosity of the universe, to surveys for black holes on all scales and the BH content of the Galaxy. The high sensitivity and angular resolution (\la5') for EXIST will allow the first full galactic survey for obscured young supernova remnants from their 68,78 keV Ti-44 emission to constrain the SN rate in the Galaxy, and the first HX imaging search for highly obscured accretion sources (including possible BHs in molecular clouds). As an all sky monitor, with instantaneous FOV of 160\degr \times 80\degr ~and full sky coverage each orbit, EXIST would be a highly sensitive next-generation GRB mission for high time/spectral/spatial resolution studies of GRBs and faint SGRs. It would also provide simultaneous HX spectra of blazars (and AGN) for comparison with \gamma-ray spectra from GLAST for constraints on the diffuse IR background. EXIST is recommended by the NAS/NRC Decadal Survey for implementation this decade, and both science and mission studies have begun. A summary will be provided in this talk.