GCN Circular 8701
M.C. Stroh and E. A. Hoversten (PSU) report on behalf of the Swift-XRT team: We have analyzed the first seven orbits of XRT data from GRB 081221 (Hoversten et al., GCN 8687) beginning 73s after the trigger. The Swift-XRT data consists of 803s in Windowed Timing (WT) mode and 5.9ks in Photon Counting (PC) mode. The enhanced XRT position for this burst was reported by Evans et al. (GCN Circ. 8690). The X-ray light curve begins with count rates near 10^3 cts/s and has an early flare reaching 1130 cts/s at T+103s. Following the flare, the light curve can be modeled with a double broken power-law with initial decay rate of 5.48 +/- 0.08, initial break time at T+207s, second decay rate of 0.68 +/- 0.20, second break time at T+896s, and a final decay rate of 1.35 +/- 0.04. If the light curve follows the same decline, we predict count rates at T+24hr and T+48hr to be 1.6e-2 and 6.4e-3 respectively. The time-averaged WT spectrum can be fit with an absorbed power law with photon index Gamma = 1.994 (+/-0.014) and nH of 3.24 (+/- 0.05) e21 cm^-2 which is in excess of the Galactic value of 2.03e20 cm^-2 (Kalberla et al. 2005). The absorbed (unabsorbed) 0.3-10.0 keV flux is 2.44 (3.86) e-9 ergs/cm^2/s. The time-averaged PC spectrum can be fit with an absorbed power law with photon index Gamma = 2.37 (+/-0.15) and nH of 3.5 (+/-0.5) e21 cm^-2. The absorbed (unabsorbed) 0.3-10.0 keV flux is 1.04 (2.17) e-11 ergs/cm^2/s. This circular is an official product of the Swift-XRT team.