期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 372, 期 1, 页码 L38-L42出版社
OXFORD UNIV PRESS
DOI: 10.1111/j.1745-3933.2006.00221.x
关键词
dust, extinction; galaxies: ISM; quasars: absorption lines; gamma-rays: bursts
We present an analysis of three strong, intervening Mg II absorption systems (z(abs) = 0.603, 0.656, 1.107) towards the optical afterglow of gamma-ray burst (GRB) 060418. From high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) spectra we measure metal column densities and find that the highest redshift absorber exhibits a large amount of dust depletion compared with damped Lyman absorbers (DLAs) seen in quasi-stellar object (QSO) spectra. The intervening z(abs) = 1.107 absorber is also unusual in exhibiting a clear 2175-angstrom bump, the first time this feature has been definitively detected in a GRB spectrum. The GRB afterglow spectrum is best fitted with a two-component extinction curve: a Small Magellanic Cloud (SMC) extinction law at z = 1.49 (the redshift of the host) with E(B - V) = 0.07 +/- 0.01 and a Galactic extinction curve at z similar to 1.1 with E(B - V) = 0.08 +/- 0.01. We also present a moderately deep New Technology Telescope (NTT) R-band image of the GRB 060418 field and spectroscopy of four galaxies within 1 arcmin. None of these objects has a redshift that matches any of the intervening absorbers, and we conclude that the galaxies responsible for the two intervening MgII absorbers at z similar to 0.6 have luminosities less than or similar to 0.3 L-star.
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