GCN Circular 12727
B.-B. Zhang and M. H. Siegel (PSU) reports on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 111225A (Siegel et al. GCN Circ. 12720), from 94 s to 23.3 ks after the BAT trigger. The data comprise 556 s 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 12724). The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=0.6 (+0.4, -0.3). At T+114 s the decay steepens to an alpha of 1.83 (+0.10, -0.09). The light curve breaks again at T+353 s to a decay with alpha=3.1 (+/-0.5), before a final break at T+590 s s after which the decay index is 1.80 (+0.11, -0.12). An early time flare (from T+214.6 to T+321.8 s) and a possible late time flare (from ~T+20000s) are excluded from the fit. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.43 (+/-0.07). The best-fitting absorption column is 2.09 (+0.16, -0.15) x 10^21 cm^-2, in excess of the Galactic value of 1.7 x 10^21 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.71 (+0.17, -0.15) and a best-fitting absorption column consistent with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.5 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 0 (+7.7, -0) x 10^20 cm^-2 Galactic foreground: 1.7 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.71 (+0.17, -0.15) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00510341. This circular is an official product of the Swift-XRT team.