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The Energetic X-ray Imaging Survey Telescope (EXIST) mission concept was selected for further study under the Astrophysics Strategic Mission Concept Study (ASMCS) program. The mission design is optimized for study of high-z GRBs as probes of the early Universe. With a 4.5 m2 imaging 5–600 keV (CZT) detector imaging a 90°×70° (>10% coding fraction) field of view with 2’ resolution and <20” (90% conf.) positions for >5σ sources, EXIST will perform rapid (<200 sec) slews onto GRBs and obtain prompt images and spectra with a co-aligned soft X-ray telescope 0.1–10 keV) and with a 1.1 m optical-IR telescope (IRT) simultaneously in 4 bands (0.3–0.52 μm, 0.52–0.9 μm, 0.9–1.38 μm, and 1.38–2.3 μm) for prompt identification (by dropouts or variability) of the GRB within a 3.75×4.25’ FoV. An autonomous spacecraft re-point (<2’) will then (at ∼300 sec after GRB trigger) put the GRB on a 0.2×10” slit for either R = 3000 (for AB <21) or R = 30 (for AB ∼21–25) prompt spectra over the 0.3–0.9 μm and 0.9–2.3 μm bands. This will provide onboard redshifts within ∼500–2000 sec for most GRBs, reaching z ∼20 (for Lyman-α breaks) if such GRBs exist, and spectra for studies of the host galaxy and local re-ionization bubble as well as intervening cosmic structure. With ∼600 GRBs/yr expected, EXIST will open a new era in studies of the early Universe as well as carry out a rich program of AGN and transient-source science. An overview of the GRB science objectives and a brief discussion of the overall mission design and operations is given, and example high-z GRB spectra are shown. EXIST is being proposed to the Astro2010 Decadal Survey as a Medium Class mission that could be launched as early as 2017. [ABSTRACT FROM AUTHOR]

The exhilerating results from Swift in its first year of operations have opened a new era of exploration of the high energy universe. The surge to higher redshifts of the Gamma-ray bursts now imaged with increased sensitivity establishes them as viable cosmic probes of the early universe. Wide-field coded aperture imaging with solid-state pixel detectors (Cd-Zn-Te) has been also established as the optimum approach for GRB discovery and location as well as to conduct sensitive full-sky hard X-ray sky surveys. I outline the current and future major science questions likely to dominate the post-Swift era for GRBs and several related disciplines and the mission requirements to tackle these. The EXIST mission, under study for NASA’s Black Hole Finder Probe (BHFP) in the Beyond Einstein Program, could achieve these objectives as the Next Generation GRB Mission with ‘ultimate’ sensitivity and wide-field survey capability. Analysis tools for processing Swift/BAT slew data are under development at CfA and will both test EXIST scanning imaging and provide new data on GRBs and transients. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]