TITLE: GCN CIRCULAR NUMBER: 13734 SUBJECT: GRB 120909A: Swift-XRT refined Analysis DATE: 12/09/09 15:55:07 GMT FROM: Phil Evans at U of Leicester V. Mangano (INAF-IASFPA), A. Melandri (INAF-OAB), M.C. Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), C. Pagani (U. Leicester), A.P. Beardmore (U. Leicester), B. Sbarufatti (INAF-OAB/PSU) and S. Immler report on behalf of the Swift-XRT team: We have analysed 9.3 ks of XRT data for GRB 120909A (Immler et al. GCN Circ. 13727), from 3.3 ks to 33.3 ks after the BAT trigger. The data comprise 173 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Osborne et al. (GCN. Circ 13732). The light curve can be modelled with a power-law decay with a decay index of alpha=1.19 (+/-0.06). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.04 (+/-0.09). The best-fitting absorption column is 1.9 (+0.8, -0.7) x 10^22 cm^-2, at a redshift of 3.93, in addition to the Galactic value of 6.5 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 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 6.5 x 10^20 cm^-2 Intrinsic column: 1.9 (+0.8, -0.7) x 10^22 cm^-2 at z=3.93 Photon index: 2.04 (+/-0.09) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00533060. This circular is an official product of the Swift-XRT team.