TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1087 SUBJECT: GRB 010222: HST observations -- host galaxy and late-time decay DATE: 01/08/14 18:45:00 GMT FROM: Andrew S. Fruchter at STScI A. Fruchter, I. Burud, J. Rhoads and A. Levan (STScI) report: We have reduced the now public archival HST images of GRB 010222, taken on 28 February, 17 and 18 March, 5 and 6 April, and 4 and 5 May of this year using the F606W (V/R) and F814W (I) filters on WFPC2. Using the most recent data, we find that OT of GRB 010222 is clearly superposed on a host galaxy. In order to accurately determine the decay of the OT and the magnitude of the host, we have drizzled the images onto an output grid that allows interlacing of these 2-point dithered images. We have then fit for the decay of the OT and the host galaxy flux using a small (~0."2) aperture, which provides the best estimate of the OT as a function of time, as well as using a larger aperture (~0."5), which is more appropriate for determining the host galaxy magnitude. We find that the late-time decay of the OT is significantly steeper than previously reported. We find a power-law decay between 28 February (day 6) and 5 May (day 71) of -1.7 +/- 0.05. Formally, we find a slightly steeper decay (-1.73 +/- 0.02) in F606W than in F814W (-1.64 +/- 0.04), but this discrepancy may indicate the level of systematic error in the slope measurement rather than true color evolution of the OT. We find that the host galaxy is dominated by a compact core (FWHM ~ 0."15) located directly under the OT. The magnitude of the host is F606W(AB) = 26.0 +/- 0.1, F814W(AB) = 25.8 +/- 0.15. Images of the host, as well as a plot of the coninuing decline of the OT, are available at http://www.stsci.edu/~fruchter/GRB/010222