Expected Number and Flux Distribution of Gamma‐Ray Burst Afterglows with High Redshifts

If Gamma-Ray-Bursts (GRBs) occur at high redshifts, then their brightafterglow emission can be used to probe the ionization and metal enrichmenthistories of the intervening intergalactic medium during the epoch ofreionization. In contrast to other sources, such as galaxies or quasars, whichfade rapidly with increasing redshift, the observed infrared flux from a GRBafterglow at a fixed observed age is only a weak function of its redshift. Thisresults from a combination of the spectral slope of GRB afterglows and thetime-stretching of their evolution in the observer's frame. Assuming that theGRB rate is proportional to the star formation rate and that the characteristicenergy output of GRBs is ~10^{52} ergs, we predict that there are always ~15GRBs from redshifts z>5 across the sky which are brighter than ~100 nJy at anobserved wavelength of ~2 \mu m. The infrared spectrum of these sources couldbe taken with the future Next Generation Space Telescope, as a follow-up ontheir early X-ray localization with the Swift satellite.Comment: 29 pages, 14 figures; submitted to Ap