If GRBs are associated with the collapse of massive stellar objects (e.g., Paczynski 1998; Woosley 1993), they are expected to be associated with star-forming regions. If this is true, photoelectric absorption and fluorescence line emission in the vicinity of GRBs might lead to observable consequences such as absorption edges and emission line features. It has been suggested that absorption edges as well as fluorescence lines and resonance-scattered burst emission could be detectable with rapid (Mészáros & Rees 1998) or long-term (Ghisellini et al. 1998) follow-up observations of GRB afterglows and thus provide a possibility for direct GRB redshift measurements. The process of time-dependent photoionization and photoelectric absorption has been studied by Perna & Loeb (1998). They focus on optical absorption lines from the CBM and suggest that temporal evolution of absorption line shapes and equivalent widths can be used to map the CBM. In a recent paper (Böttcher et al. 1999), we adopted a similar approach to the one used by Perna & Loeb (1998), but additionally implemented the Auger process and fluorescence line emission following inner-shell ionization events, and used a realistic representation of the temporal evolution of the GRB radiation. Here we give a short summary of the main results of this analysis, focusing on observable effects in the X-ray regime.
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