GCN Circular 12543
Bin-Bin Zhang (PSU) reports on behalf of the Swift-XRT team: We have analysed 12 ks of XRT data for GRB 111107A (Siegel et al. GCN Circ. 12534), from 55 s to 30.6 ks after the BAT trigger. The data comprise 42 s in Windowed Timing (WT) mode (the first 7 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN. Circ 12538). The late-time light curve (from T0+5.1 ks) can be modelled with a power-law decay with a decay index of alpha=1.12 (+0.29, -0.27). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.15 (+0.12, -0.16). The best-fitting absorption column is 3.5 (+6.0, -3.5) x 10^21 cm^-2, at a redshift of 2.893, in addition to the Galactic value of 8.9 x 10^20 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 8.9 x 10^20 cm^-2 Intrinsic column: 3.5 (+6.0, -3.5) x 10^21 cm^-2 at z=2.893 Photon index: 2.15 (+0.12, -0.16) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00507185. This circular is an official product of the Swift-XRT team.