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Title: The line-of-sight towards GRB 030429 at z = 2.66: Probing the matter at stellar, galactic and intergalactic scales
Authors: Jakobsson, P.
Hjorth, J.
Fynbo, J. P. U.
Watson, D.
Pedersen, K.
Jensen, B. L.
Jakobsson, P.
Björnsson, G.
Gudmundsson, E. H.
Fynbo, J. P. U.
Weidinger, M.
Weidinger, M.
Møller, P.
Gorosabel, J.
Castro-Tirado, A. J.
Gorosabel, J.
Cerón, J. M. C.
Fruchter, A.
Ledoux, C.
Wijers, R. A. M. J.
Sollerman, J.
Henden, A. A.
Gilmore, A.
Kilmartin, P.
Levan, A.
Masetti, N.
Tanvir, N.
First Published: Dec-2004
Publisher: EDP Sciences for European Southern Observatory (ESO)
Citation: Astronomy & Astrophysics, 2004, 427 (3), pp. 785-794
Abstract: We report the discovery of the optical afterglow (OA) of the long-duration gamma-ray burst GRB 030429, and present a comprehensive optical/near-infrared dataset used to probe the matter at different distance scales, i.e. in the burst environment, in the host galaxy and in an intervening absorber. A break in the afterglow light curve is seen approximately 1 day from the onset of the burst. The light curve displays a significant deviation from a simple broken power-law with a bright 1.5 mag bump with a duration of 2-3 days. The optical/near-infrared spectral energy distribution is best fit with a power-law with index $\beta = -0.36$ $\pm$ 0.12 reddened by an SMC-like extinction law with (a modest) AV = 0.34 $\pm$ 0.04. In addition, we present deep spectroscopic observations obtained with the Very Large Telescope. The redshift measured via metal absorption lines in the OA is z = 2.658 $\pm$ 0.004. Based on the damped Ly $\alpha$ absorption line in the OA spectrum we measure the $\ion{H}{i}$ column density to be $\log N(\ion{H}{i}) = 21.6$ $\pm$ 0.2. This confirms the trend that GRBs tend to be located behind very large $\ion{H}{i}$ column densities. The resulting dust-to-gas ratio is consistent with that found in the SMC, indicating a low metallicity and/or a low dust-to-metal ratio in the burst environment. We find that a neighbouring galaxy, at a separation of only $1\farcs2$, has z = 0.841 $\pm$ 0.001, ruling it out as the host of GRB 030429. The small impact parameter of this nearby galaxy, which is responsible for $\ion{Mg}{ii}$ absorption in the OA spectrum, is in contrast to previous identifications of most QSO absorption-selected galaxy counterparts. Finally, we demonstrate that the OA was not affected by strong gravitational lensing via the nearby galaxy.
DOI Link: 10.1051/0004-6361:20041233
ISSN: 0004-6361
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Copyright © 2004 ESO. Reproduced with permission from Astronomy & Astrophysics, © ESO.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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