Damped Lyalpha Systems in GRB Afterglows

We present VLT spectroscopy of the afterglow of GRB 030323, which shows a damped Lyα (DLA) absorption line at a redshift z=3.372 with an inferred neutral hydrogen column density of log N(HI)=21.90±0.07, larger than any (GRB‐ or QSO‐) DLA HI column density inferred directly from Lyα in absorption. We discuss several other properties of the GRB host, such as the metallicity ([S/H]=−1.3±0.2), the H2 content, and the detection of SiII*, which has never been clearly detected in QSO‐DLAs. From the latter we infer an order of magnitude estimate for the particle density: nH0 ∼ 100 cm−3. Comparison of the HI column densities and metallicities in the available sample of GRB‐DLAs (which is still very small) with those in the sample of QSO‐DLAs suggests that both of these quantities are larger in GRB‐DLAs.