TITLE: GCN CIRCULAR NUMBER: 13053 SUBJECT: GRB 120312A: Swift-XRT refined Analysis DATE: 12/03/13 04:34:08 GMT FROM: Phil Evans at U of Leicester V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), O.M. Littlejohns (U. Leicester) and M. Stamatikos report on behalf of the Swift-XRT team: We have analysed 9.9 ks of XRT data for GRB 120312A (Stamatikos et al. GCN Circ. 13049), from 112 s to 19.6 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 2188 s of PC mode data and 2 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 = 251.78816, +23.85817 which is equivalent to: RA (J2000): 16h 47m 09.16s Dec(J2000): +23d 51' 29.4" with an uncertainty of 1.6 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.28 (+0.14, -0.13). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.54 (+0.26, -0.25). The best-fitting absorption column is 1.4 (+0.9, -0.8) x 10^21 cm^-2, in excess of the Galactic value of 4.1 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 4.9 x 10^-11 (5.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.4 (+0.9, -0.8) x 10^21 cm^-2 Galactic foreground: 4.1 x 10^20 cm^-2 Excess significance: 2.1 sigma Photon index: 1.54 (+0.26, -0.25) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00517566. This circular is an official product of the Swift-XRT team.