GCN Circular 12092
K. L. Page (U Leicester) reports on behalf of the Swift-XRT team: We have analysed 4.1 ks of XRT data for GRB 110625A (Page et al. GCN Circ. 12088), from 129 s to 34.9 ks after the BAT trigger. The data comprise 96 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 best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 286.7327, 6.7553 which is equivalent to: RA (J2000): 19 06 55.85 Dec(J2000): +06 45 19.2 with an uncertainty of 2.1 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=1.12 (+0.04, -0.03), followed by a break at T+18.7 ks to an alpha of 2.7 (+7.3, -1.2). There are insufficient data to constrain this steeper decay well at this time. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+/-0.4). The best-fitting absorption column is 6.3 (+1.1, -1.0) x 10^22 cm^-2, in excess of the Galactic value of 1.4 x 10^22 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 1.8 (+/-0.4) and a best-fitting absorption column of 5.9 (+1.3, -1.1) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 1.1 x 10^-10 (3.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 5.9 (+1.3, -1.1) x 10^22 cm^-2 Galactic foreground: 1.4 x 10^22 cm^-2 Excess significance: 8.7 sigma Photon index: 1.8 (+/-0.4) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00456073. This circular is an official product of the Swift-XRT team.