GCN Circular 12643
D. Grupe (PSU) and E. A. Hoversten (PSU) reports on behalf of the Swift-XRT team: We have analyzed 11 ks of XRT data for GRB 111209A (Hoversten et al. GCN Circ. 12632), from 425 s to 25.2 ks after the BAT trigger. The data comprise 9.4 ks in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN. Circ 12639). The light curve can be modeled with a series of power-law decays. The light curve initially rises, with an index alpha=-0.21 (+/-0.04). At T+864 s it breaks to an alpha of 7.3 (+0.7, -2.6). The light curve breaks again at T+899 s to a decay with alpha=0.679 (+0.012, -0.087), and again at T+5807 s s to alpha=1.179 (+/-0.016), before a final break at T+19.4 ks s after which the decay index is 6.3 (+1.2, -0.4). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.333 (+/-0.012). The best-fitting absorption column is 1.38 (+/-0.04) x 10^21 cm^-2, in excess of the Galactic value of 1.5 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.83 (+0.17, -0.16) and a best-fitting absorption column of 1.3 (+0.5, -0.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.1 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.3 (+0.5, -0.4) x 10^21 cm^-2 Galactic foreground: 1.5 x 10^20 cm^-2 Excess significance: 4.4 sigma Photon index: 1.83 (+0.17, -0.16) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00509336. This circular is an official product of the Swift-XRT team.