TITLE: GCN CIRCULAR NUMBER: 15441 SUBJECT: GRB 131103A: Swift-XRT refined Analysis DATE: 13/11/04 12:20:15 GMT FROM: Phil Evans at U of Leicester D.N. Burrows (PSU), J.A. Kennea (PSU), V. Mangano (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and J.R. Cummings report on behalf of the Swift-XRT team: We have analysed 9.1 ks of XRT data for GRB 131103A (Cummings et al. GCN Circ. 15440), from 82 s to 25.5 ks after the BAT trigger. The data comprise 793 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 348.9213, -44.6377 which is equivalent to: RA (J2000): 23 15 41.11 Dec(J2000): -44 38 15.7 with an uncertainty of 3.5 arcsec (radius, 90% confidence). The late-time light curve (from T0+5.9 ks) can be modelled with a power-law decay with a decay index of alpha=1.16 (+/-0.26). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.76 (+0.27, -0.25). The best-fitting absorption column is 4.0 (+0.8, -0.7) x 10^21 cm^-2, in excess of the Galactic value of 1.1 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.15 (+0.18, -0.17) and a best-fitting absorption column of 3.5 (+0.7, -0.6) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (7.2 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.5 (+0.7, -0.6) x 10^21 cm^-2 Galactic foreground: 1.1 x 10^20 cm^-2 Excess significance: 8.9 sigma Photon index: 2.15 (+0.18, -0.17) If the light curve continues to decay with a power-law decay index of 1.16, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x 10^-13 (4.6 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/00576562. This circular is an official product of the Swift-XRT team.