GRB redshift determination in the X-ray band

If gamma-ray bursts originate in dense stellar forming regions, the interst ellar material can imprint detectable absorption features on the observed X -ray spectrum. Such features can be detected by existing and planned X-ray satellites, as long as the X-ray afterglow is observed after a few minutes from the burst. Detection of these X-ray features will make possible the de termination of the redshift of gamma-ray bursts even when their optical aft erglows are severely dimmed by extinction. For further detail see Ghisellin i et al. (1999).