TITLE: GCN CIRCULAR NUMBER: 13724 SUBJECT: GRB 120907A: Swift-XRT refined Analysis DATE: 12/09/07 16:38:07 GMT FROM: Phil Evans at U of Leicester A. Maselli (INAF-IASFPA), V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), M.C. Stroh (PSU), D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester) and J.L. Racusin report on behalf of the Swift-XRT team: We have analysed 16 ks of XRT data for GRB 120907A (Racusin et al. GCN Circ. 13716), from 93 s to 46.4 ks after the BAT trigger. The data comprise 76 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 13722). The late-time light curve (from T0+4.5 ks) can be modelled with a power-law decay with a decay index of alpha=1.02 (+/-0.08). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.91 (+0.13, -0.12). The best-fitting absorption column is 10.0 (+3.1, -2.9) x 10^20 cm^-2, in excess of the Galactic value of 5.4 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 3.8 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 10.0 (+3.1, -2.9) x 10^20 cm^-2 Galactic foreground: 5.4 x 10^20 cm^-2 Excess significance: 2.7 sigma Photon index: 1.91 (+0.13, -0.12) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00532871. This circular is an official product of the Swift-XRT team.