GCN Circular 4160
J. Racusin, C. Pagani, D. Morris, A. Retter, D. Burrows (PSU), N. Gehrels (GSFC) on behalf of the Swift XRT team: We have analyzed the first 13 orbits of data from GRB051021B (Retter et al., GCN 4126). XRT observations began in Window Timing mode 87 seconds after the BAT trigger and continued for 32 seconds before switching to Photon Counting mode. The XRT light curve shows an initial decline with a decay slope of 1.9+/-0.1 , followed by a break at ~T+2500s to a shallower decay slope of 0.6+/-0.1. A preliminary spectral fit using an absorbed power-law to the Photon Counting mode data yields a photon index of 1.64+/-0.12 in the 0.85-10 keV band, fixing nH to the Galactic value of 7.7E21 cm-2. The observed 0.85-10 keV flux for the Photon Counting mode data in the first orbit is 7.3E-12 ergs cm-2 s-1 corresponding to an unabsorbed flux of 9.0E-12 ergs cm-2 s-1.