UVES ‐ VLT High Resolution Spectroscopy of GRB Afterglows

We present early time, high resolution spectroscopy of three GRB afterglows: GRB050730, GRB050922C and GRB060418. These data give us precious information on the kinematics, ionization and metallicity of the interstellar matter of GRB host galaxies up to a redshift z ∼ 4, and of intervening absorbers along the line of sight.In particular, we find that the GRB surrounding medium is complex, featuring a clumpy environment in which gas is distributed in regions of space with different distances from the GRB explosion site. The absorption spectra show that elements are present both with high and low ionization states, and even forbidden, fine structure levels are commonly observed. These features allow us to evaluate the physical parameters of the absorbing gas. In details, the density of the gas regions lie in the range n = 10 ÷ 106 cm−3, and the temperatures are of the order of T = 103 ÷ 104 K.The metallicity of the GRB host galaxies is computed using the hydrogen absorption features. We find undersolar abun...