Heavy‐Element Abundances and Dust Depletions in the Host Galaxies of Three Gamma‐Ray Bursts

Abstract

We have derived the column densities of heavy elements in three gamma-ray burst (GRB) optical transients, associated with the circumburst or interstellar medium (ISM) of the host galaxy. In comparison with the same elements observed in damped Lyα (DLA) systems along QSO sight lines, we find evidence for much higher column densities of Zn II. The gap between the QSO-DLA and GRB-DLA distributions is smoothly bridged by observations of the interstellar absorption in the Milky Way and the Magellanic Clouds. Very small [Fe/Zn], [Si/Zn], and [Cr/Zn] values in GRB-DLAs indicate large dust depletions. Once the dust-to-metals ratios are determined, we find an optical extinction AV~1 mag, to be compared with typical AV