TITLE: GCN CIRCULAR NUMBER: 14112 SUBJECT: GRB 121226A: Swift-XRT refined Analysis DATE: 12/12/27 18:24:04 GMT FROM: Phil Evans at U of Leicester O.M. Littlejohns (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), G. Stratta (ASDC), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J.A. Kennea (PSU), M.C. Stroh (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and H.A. Krimm report on behalf of the Swift-XRT team: We have analysed 10 ks of XRT data for GRB 121226A (Krimm et al. GCN Circ. 14105), from 109 s to 35.4 ks after the BAT trigger. The data are entirely 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 = 168.6423, -30.4064 which is equivalent to: RA (J2000): 11 14 34.14 Dec(J2000): -30 24 23.1 with an uncertainty of 2.1 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=0.98 (+/-0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.4 (+/-0.4). The best-fitting absorption column is 8.2 (+2.5, -2.1) x 10^21 cm^-2, in excess of the Galactic value of 6.1 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 4.4 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 8.2 (+2.5, -2.1) x 10^21 cm^-2 Galactic foreground: 6.1 x 10^20 cm^-2 Excess significance: 6.0 sigma Photon index: 2.4 (+/-0.4) If the light curve continues to decay with a power-law decay index of 0.98, the count rate at T+24 hours will be 1.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.7 x 10^-14 (1.9 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/00544027. This circular is an official product of the Swift-XRT team.