Long gamma-ray bursts (GRBs) are the most luminous known electromagnetic radiation sources in the Universe for the ~3 - 300 sec of their prompt flashes (isotropic X/γ -ray luminosities up to ~1053 erg s-1). Their afterglows have first day rest-frame UV/optical absolute magnitudes AB ~ -30 - -23. This luminous continuum nUV-nIR back-light provides the ultimate probe of the SFR(z) back to the first Pop III-II.5 stars, expected to be massive and GRB progenitors. GRB afterglow spectra in the first ~1-3 hours will directly measure their host galaxy ionization fraction xi vs. z in the Epoch of Reionization (EOR), tracing the growth of structure. Only 28% of Swift GRBs have measured redshifts due to limited followup at R, J <21. Some ~25% of GRBs are optically dark due to dust absorption in their host galaxies, but those with low NH in their X-ray spectra are likely at z >7. Current 8-10m telescopes and coming ELTs cannot pursue optically dark GRBs promptly, nor can JWST or WFIRST slew within ~0.5-1 days of a GRB. The Time-domain Spectroscopic Observatory (TSO) is a proposed Probe-class 1.3m telescope at L2, with imaging and spectroscopy (R = 200, 1800) in 4 bands (0.3 - 5µm) and rapid slew capability to 90% of sky. TSO would finally utilize z > 6 - 12 GRBs as the most direct probe of the SFR(z), EOR(z), and possibly the first direct detection of the core collapse of the very first (Pop III) stars.
|Original language||English (US)|
|State||Published - Mar 19 2019|
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