GCN Circular 15968
L. Izzo (URoma/ICRA), V. D'Elia (ASDC) and J. L. Racusin (NASA/GSFC) report on behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for GRB 140311A (Racusin et al. GCN Circ. 15944), from 9.5 ks to 57.1 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 2850 s of PC mode data and 7 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 = 209.30521, +0.64191 which is equivalent to: RA (J2000): 13h 57m 13.25s Dec(J2000): +00d 38' 30.9" with an uncertainty of 1.5 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.13 (+0.16, -0.14). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.61 (+0.17, -0.12). The best-fitting absorption column is consistent with the Galactic value of 2.8 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 3.9 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 2.8 x 10^20 cm^-2 Intrinsic column: 0 (+2.2, -0) x 10^22 cm^-2 at z=4.95 Photon index: 1.61 (+0.17, -0.12) If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 0.013 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x 10^-13 (5.3 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00591390 This circular is an official product of the Swift-XRT team.