Abstract
We present the first high-resolution (R ¼ 20;000 45;000, corresponding to 14 km s � 1 at 4200 8 to 6.6 km s � 1 at 9000 8) observations of the optical afterglow of gamma-ray bursts. GRB 020813 and GRB 021004 were observed by UVES at the Very Large Telescope 22.19 and 13.52 hr after the trigger, respectively. These spectra show that the interstellar matter of the GRB host galaxies is complex, with many components contributing to each main absorption system, and spans a total velocity range of up to about 3000 km s � 1 . Several narrow components are resolved down to aw idth of af ew tens of km s � 1 . In the case of GRB 021004 we detected both low- and highionization lines. Combined with photoionization results obtained with CLOUDY, the ionization parameters of the varioussystemsareconsistentwitharemarkablynarrowrangewithnocleartrendwithsystemvelocity.Thiscanbe interpreted as due to density fluctuations on top of a regular R � 2 wind density profile. Subject headingg cosmology: observations — galaxies: abundances — galaxies: ISM — gamma rays: bursts Online material: color figures
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