GCN Circular 11916
C. W. Wolf (PSU) reports on behalf of the Swift-XRT team: We have analysed 26 ks of XRT data for GRB 110407A (Wolf et al. GCN Circ. 11894), from 147 s to 272.1 ks after the BAT trigger. The data comprise 593 s in Windowed Timing (WT) mode (the first 10 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 Evans et al. (GCN. Circ 11896). After initial flaring (T>0.9 ks), the light curve can be modeled by a broken power-law model, with an initial decay index of alpha1=2.19 (+0.12, -0.11). A break occurs at T+13.6 ks followed by a plateau phase with a decay index of alpha2 = 0.4 (+0.5, -0.7). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+/-0.05). The best-fitting absorption column is 1.00 (+/-0.13) x 10^21 cm^-2, in excess of the Galactic value of 2.0 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.87 (+0.21, -0.11) and a best-fitting absorption column of 8.4 (+5.1, -2.7) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.2 x 10^-11 (5.0 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.4 (+5.1, -2.7) x 10^20 cm^-2 Galactic foreground: 2.0 x 10^20 cm^-2 Excess significance: 5.2 sigma Photon index: 1.87 (+0.21, -0.11) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00450884. This circular is an official product of the Swift-XRT team.