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A. Loeb (IAS, Princeton and Harvard University)
Gamma-Ray Burst (GRB) afterglows offer better prospects for probing the epoch of reionization than traditional sources such as quasars or galaxies. The Swift satellite will localize of order a hundred GRBs per year. About 10--25% of these sources are expected to originate at redshifts z>5. High-redshift GRBs can be easily identified through infrared photometry, based on the Lyman-alpha trough in their spectrum due to absorption by intergalactic hydrogen along the line-of-sight. Follow-up spectroscopy of the high-redshift GRB candidates could then be done on 10-meter class telescopes.
The afterglow flux at a given (observed) time lag after the gamma-ray trigger, is not expected to fade significantly with increasing redshift because higher redshifts translate to earlier times in the source frame during which the afterglow is intrinsically brighter. Unlike quasars, GRB afterglows do not ionize their intergalactic environment and their low-mass host galaxies are not likely to perturb gravitationally the Hubble flow around them. Afterglow spectroscopy therefore provides an ideal probe of the damping wing of the Gunn-Peterson trough.
Swift will possibly detect GRBs from the very first generation of stars that formed in the universe. As such it will shed light on the process of early star formation and metal enrichment that so far has been treated only theoretically.
Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.