TITLE: GCN CIRCULAR NUMBER: 15311 SUBJECT: GRB 131004A: Swift-XRT refined Analysis DATE: 13/10/05 11:54:05 GMT FROM: Phil Evans at U of Leicester C. Pagani (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Maselli (INAF-IASFPA), D.N. Burrows (PSU), J.A. Kennea (PSU), V. Mangano (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and report on behalf of the Swift-XRT team: report on behalf of the Swift-XRT team: We have analysed 9.1 ks of XRT data for GRB 131004A, from 79 s to 34.7 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. the light curve is consistent with a constant source of mean count rate 7.4e-02 ct/sec. A power-law fit gives an index of 0.1 (+2.0, -1.6). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.16 (+0.27, -0.26). The best-fitting absorption column is 3.1 (+1.0, -0.9) x 10^21 cm^-2, in excess of the Galactic value of 7.0 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 (6.8 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+1.0, -0.9) x 10^21 cm^-2 Galactic foreground: 7.0 x 10^20 cm^-2 Excess significance: 4.7 sigma Photon index: 2.16 (+0.27, -0.26) If the light curve continues to decay with a power-law decay index of 0.1, the count rate at T+24 hours will be 0.029 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-12 (1.9 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00573190. This circular is an official product of the Swift-XRT team.