Damped Lyman Alpha (DLA) Systems in GRBAfterglows: Probing Dense Regions in GRB Host Galaxies

摘要

To date, only a handful of Damped Lyman alpha systems havebeen detected in GRB afterglows, and roost of these have modest signal-to-noiseratios. Our detection of a DLA in the afterglow of GRB 030323 is unambiguous:its neutral hydrogen column density is log N(HI)=21.90±0.07, higher than any(GRB or QSO) DLA H I column density inferred directly from Lya, in absorption.We discuss several other properties, such as the metallicity, the detection of fine-structure lines of Si II, and our strong upper limit on the 112 content. The GRBafterglow allows us to infer all these quantities, even with the host being as faintas V=28. The upcoming launch of the Swift satellite will make high-resolutionspectroscopy of a large sample of GRB afterglows possible. This will offer aunique way to study in detail the interstellar medium inside GRB host galaxiesas a function of redshift.