Hubble Space Telescope and Ground-based Optical and Ultraviolet Observations of GRB 010222

Abstract

We report on Hubble Space Telescope (HST) Wide Field Planetary Camera 2 optical and Space Telescope Imaging Spectrograph (STIS) near- ultraviolet MAMA observations and ground-based optical observations of GRB 010222, spanning 15 hr to 71 days. The observations are well described by a relativistic blast wave model with a hard electron energy distribution, p=1.57${}^{+}0.04$${}_{-}0.03$, and a jet transition at t${}_{\ast }$=0.93${}^{+}0.15$${}_{-}0.06$ days. These values are slightly larger than previously found as a result of a correction for the contribution from the host galaxy to the late-time ground-based observations and the larger temporal baseline provided by the HST observations. The host galaxy is found to contain a very compact core (size <0.25’'), which coincides with the position of the optical transient. The STIS near-ultraviolet MAMA observations allow for an investigation of the extinction properties along the line of sight to GRB 010222. We find that the far-ultraviolet curvature component c${}_4$ is rather large. In combination with the low optical extinction, A${}_V$=0.110${}^{+}0.010$${}_{-}0.021$ mag, when compared with the hydrogen column inferred from X-ray observations, we suggest that this is evidence for dust destruction.