Redshift determination in the X-ray band of gamma-ray bursts

If gamma-ray bursts originate in dense star-forming regions, the interstell ar material can imprint detectable absorption features on the observed X-ra y spectrum. Such features can be detected by existing and planned X-ray sat ellites, as long as the X-ray afterglow is observed within a few minutes of the burst. If the column density of the interstellar material exceeds simi lar to 10(23) cm(-2) there exists a possibility of detecting the K alpha fl uorescent iron line, which should be visible for more than 1 yr, long after the X-ray afterglow continuum has faded away. Detection of these X-ray fea tures will make possible the determination of the redshift of gamma-ray bur sts even when their optical afterglow is severely dimmed by extinction.