GCN Circular 12658
C. A. Wolf (PSU) reports on behalf of the Swift-XRT team: We have analysed 4.5 ks of XRT data for the Swift/BAT ground-detected burst: GRB 111208A (Sakamoto et al. GCN Circ. 12628), from 24.3 ks to 40.8 ks after the burst. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Swift/BAT error circle. Using 4204 s of PC mode data and 6 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 290.22434, +40.67616 which is equivalent to: RA (J2000): 19h 20m 53.84s Dec(J2000): +40d 40' 34.2" with an uncertainty of 1.6 arcsec (radius, 90% confidence). This position is 37 arcsec from the Swift/BAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=3.14 (+0.23, -0.90). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.14 (+0.25, -0.37). The best-fitting absorption column is 1.7 (+1.1, -0.9) x 10^21 cm^-2, consistent with the Galactic value of 8.4 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 3.5 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.7 (+1.1, -0.9) x 10^21 cm^-2 Galactic foreground: 8.4 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 2.14 (+0.25, -0.37) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020190 . This circular is an official product of the Swift-XRT team.