EXIST: All-sky hard X-ray imaging and spectral-temporal survey for black holes

The energetic X-ray imaging survey telescope (EXIST) is under study for the proposed Black Hole Finder Probe, one of the three Einstein Probe missions in NASA's proposed Beyond Einstein Program. EXIST would have unique capabilities: it would survey the full sky at 5-600 keV each 95 min orbit with 0.9-5′, 10 μs-45 min and ∼0.5-5 keV resolution to locate sources to 10″ and enable black holes to be surveyed and studied on all scales. With a 1y/5σ survey sensitivity Fx (40-80 keV) ∼ 5 × 10−13 erg cm−2 s−1, comparable to the ROSAT soft X-ray (0.3-2.5 keV) sky survey, a large sample (≳2-4 × 104) of obscured AGN will be identified and a complete sample of accreting stellar mass BHs in the Galaxy will be found. The all-sky/all-time coverage will allow rare events to be measured, such as possible stellar disruption flares from dormant AGN out to ∼100 Mpc. A large sample (∼2-3/day) of GRBs will be located (≲10″) at sensitivities and bandwidths much greater than previously and likely yield the highest redshift events and constraints on Pop III BHs. An outline of the mission design from the ongoing concept study is presented.