ProtoEXIST

ProtoEXIST is a balloon-borne wide-field hard X-ray survey project, which is a prototype experiment for a next generation hard X-ray survey mission - the Energetic X-ray Imaging Survey Telescope (EXIST). EXIST was recommended by the 2001 Decadal Survey and further developed as a candidate for Black Hole Finder Probe (BHFP) under the NASA Beyond Einstein program and then for the 2010 Decadal Survey. Although not recommended (on cost grounds) by the Astro2010 Survey, the science objectives and capabilities of EXIST are consistent with priorities recommended in the Astro2010 Survey Report and Panel Reports. A Hard X-ray (5-100 keV; with response to 200 keV) imaging survey of at least half the sky is needed for 1) A high resolution (5X finer than Swift/BAT) survey of the Galactic Bulge and full southern galactic plane to locate transients, obscured black holes and Ti-44 sources for followup with NuSTAR and Astro-H, 2) Time Domain Astrophysics studies of the Bulge, southern Plane and North Galactic Pole with coverage each 96min orbit, and 3) Broader-band, higher spatial resolution studies of GRBs, with identification of Advanced LIGO short GRBs as well as novel opportunities for ground-based 24h coverage of southern-sky GRBs.