Very high column density and small reddening towards GRB 020124 at z = 3.20
Abstract
We present optical and near-infrared observations of the dim afterglow of GRB 020124, obtained between 2 and 68 hours after the gamma-ray burst. The burst occurred in a very faint (R > 29.5) Damped Ly-alpha Absorber (DLA) at a redshift of z = 3.198 +- 0.004. The derived column density of neutral hydrogen is log(N_H) = 21.7 +- 0.2 and the rest-frame reddening is constrained to be E(B-V) < 0.065, i.e., A_V < 0.20 for standard extinction laws with R_V ~ 3. The resulting dust-to-gas ratio is less than 11 % of that found in the Milky Way, but consistent with the SMC and high-redshift QSO DLAs, indicating a low metallicity and/or a low dust-to-metals ratio in the burst environment. A grey extinction law (large R_V), produced through preferential destruction of small dust grains by the GRB, could increase the derived A_V and dust-to-gas ratio. The dimness of the afterglow is however fully accounted for by the high redshift: If GRB 020124 had been at z = 1 it would have been approximately 1.8 mag brighter--in the range of typical bright afterglows.
Keywords
Cite
@article{arxiv.astro-ph/0307331,
title = {Very high column density and small reddening towards GRB 020124 at z = 3.20},
author = {J. Hjorth and P. Møller and J. Gorosabel and J. P. U. Fynbo and S. Toft and A. O. Jaunsen and A. A. Kaas and T. Pursimo and K. Torii and T. Kato and H. Yamaoka and A. Yoshida and B. Thomsen and M. I. Andersen and I. Burud and J. M. Castro Cerón and A. J. Castro-Tirado and A. S. Fruchter and L. Kaper and C. Kouveliotou and N. Masetti and E. Palazzi and H. Pedersen and E. Pian and J. Rhoads and E. Rol and N. R. Tanvir and P. M. Vreeswijk and R. A. M. J. Wijers and E. P. J. van den Heuvel},
journal= {arXiv preprint arXiv:astro-ph/0307331},
year = {2008}
}
Comments
23 pages, 6 figures, ApJ, in press