Vol. 571
In section 6. Interstellar and circumstellar matter

The mysterious optical afterglow spectrum of GRB 140506A at z = 0.889

by J.P.U. Fynbo, T. Krühler, K. Leighly, et al. A&A 572, A12


Gamma-ray bursts (GRBs) are powerful tools used to probe the interstellar medium of distant star-forming galaxies. The present work tries to clarify the mystery of the peculiar afterglow spectrum of the z = 0.889 GRB 140506A. Using spectroscopy with ESO/X-shooter at several epochs after the burst and imaging and spectroscopy of the host galaxy obtained with the Magellan telescope, the authors try to understand the origin of the very unusual properties of the absorption towards this GRB. It appears that there are several components aligned along the line of sight: first, a very broad and strong dust extinction in the visible associated with Balmer lines and variable between the two epochs; second, an HII region, detected with H and He excited absorption lines; third, a cooler region detected by molecular absorption from CH+. All three components have different velocities.