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.Comment: 23 pages, 6 figures, ApJ, in pres