The Bright Gamma‐Ray Burst of 2000 February 10: A Case Study of an Optically Dark Gamma‐Ray Burst

The gamma-ray burst GRB000210 had the highest gamma-ray peak flux of anyevent localized by BeppoSAX as yet but it did not have a detected opticalafterglow. It is therefore one of the events recently classified as dark GRBsor GHOST (GRB Hiding Optical Source Transient), whose origin is still unclear.Chandra observations allowed us to localize this GRB within ~1" and a radiotransient was detected with the VLA. We identify the likely (P=0.01) hostgalaxy of this burst at z=0.846. The X-ray spectrum of the afterglow showsintrinsic absorption N_H=5x10**21 cm-2. The amount of dust needed to absorb theoptical flux of this object is consistent with the above HI column density,given a dust-to-gas ratio similar to that of our Galaxy. We do not findevidence for a partially ionized absorber expected if the absorption takesplace in a Giant Molecular Cloud. We therefore conclude that either the gas islocal to the GRB, but is condensed in small-scale high-density (n>~10**9 cm-3)clouds, or that the GRB is located in a dusty, gas-rich region of the galaxy.Finally, if GRB000210 lies at z>5, its X-ray absorbing medium would have to besubstantially different from that observed in GRBs with optical afterglows.Comment: 29 pages, 7 fig.s, some revisions, ApJ, in pres