The Faint Optical Afterglow and Host Galaxy of GRB 020124: Implications for the Nature of Dark Gamma‐Ray Bursts

We present ground-based optical observations of GRB 020124 starting 1.6 hoursafter the burst, as well as subsequent Very Large Array (VLA) and Hubble SpaceTelescope (HST) observations. The optical afterglow of GRB 020124 is one of thefaintest afterglows detected to date, and it exhibits a relatively rapid decay,$F_\nu\propto t^{-1.60\pm 0.04}$, followed by further steepening. In addition,a weak radio source was found coincident with the optical afterglow. The HSTobservations reveal that a positionally coincident host galaxy must be thefaintest host to date, R>29.5 mag. The afterglow observations can be explainedby several models requiring little or no extinction within the host galaxy,A_V~0-0.9 mag. These observations have significant implications for thestatistics of the so-called dark bursts (bursts for which no optical afterglowis detected), which are usually attributed to dust extinction within the hostgalaxy. The faintness and relatively rapid decay of the afterglow of GRB020124, combined with the low inferred extinction indicate that some darkbursts are intrinsically dim and not dust obscured. Thus, the diversity in theunderlying properties of optical afterglows must be observationally determinedbefore substantive inferences can be drawn from the statistics of dark bursts.Comment: Submitted to ApJ; 13 pages; 4 tables; 5 figure