GCN Circular 12442
V. Mangano (INAF-IASFPA) reports on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 111016A (Mangano et al. GCN Circ. 12439), from 185 s to 23.8 ks after the BAT trigger. The data comprise 693 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 12441). The late-time light curve (from T0+4.1 ks) can be modelled with an initial power-law decay with an index of alpha=3.62 (+0.24, -0.98), followed by a break at T+5533 s to an alpha of 1.06 (+0.15, -0.23). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.800 (+/-0.024). The best-fitting absorption column is 1.85 (+/-0.07) x 10^21 cm^-2, in excess of the Galactic value of 2.5 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.23 (+0.09, -0.14) and a best-fitting absorption column of 7.3 (+2.2, -3.3) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.2 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 7.3 (+2.2, -3.3) x 10^20 cm^-2 Galactic foreground: 2.5 x 10^20 cm^-2 Excess significance: 3.6 sigma Photon index: 2.23 (+0.09, -0.14) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00505646. This circular is an official product of the Swift-XRT team.