Very high column density and small reddening towards GRB 020124 at z = 3.20

J. Hjorth; P. Møller; J. Gorosabel; J. P. U. Fynbo; S. Toft; A. O. Jaunsen; A. A. Kaas; T. Pursimo; K. Torii; T. Kato; H. Yamaoka; A. Yoshida; B. Thomsen; M. I. Andersen; I. Burud; J. M. Castro Cerón; A. J. Castro-Tirado; A. S. Fruchter; L. Kaper; C. Kouveliotou; N. Masetti; E. Palazzi; H. Pedersen; E. Pian; J. Rhoads; E. Rol; N. R. Tanvir; P. M. Vreeswijk; R. A. M. J. Wijers; E. P. J. van den Heuvel

doi:10.1086/378493

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Very high column density and small reddening towards GRB 020124 at z = 3.20

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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.

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J. Hjorth, P. Møller, J. Gorosabel, J. P. U. Fynbo, S. Toft, A. O. Jaunsen, A. A. Kaas, T. Pursimo, K. Torii, T. Kato, H. Yamaoka, A. Yoshida, B. Thomsen, M. I. Andersen, I. Burud, J. M. Castro Cerón, A. J. Castro-Tirado, A. S. Fruchter, L. Kaper, C. Kouveliotou, N. Masetti, E. Palazzi, H. Pedersen, E. Pian, J. Rhoads, E. Rol, N. R. Tanvir, P. M. Vreeswijk, R. A. M. J. Wijers, E. P. J. van den Heuvel. 2003-07-17. Very high column density and small reddening towards GRB 020124 at z = 3.20. https://doi.org/10.1086/378493

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