Observations of GRBs at High Redshift

The extreme luminosity of gamma-ray bursts (GRBs) and their afterglows means they are detectable, in principle, to very high redshifts. Although the redshift distribution of GRBs is difficult to determine, due to incompleteness of present samples, we argue that for Swift-detected bursts the median redshift is between 2.5 and 3, with a few percent likely at z > 6. Thus, GRBs are potentially powerful probes of the era of reionization, and the sources responsible for it. Moreover, it seems likely that they can provide constraints on the star formation history of the universe, and may also help in the determination of the cosmological parameters