TITLE: GCN CIRCULAR NUMBER: 8561 SUBJECT: GRB 081126: Swift-XRT refined analysis DATE: 08/11/27 12:04:20 GMT FROM: Raffaella Margutti at U. di Milano Bicocca R. Margutti (Univ. Bicocca & INAF-OAB) reports on behalf of the Swift XRT team: We have analysed the first 5 orbits of Swift-XRT data obtained for GRB 081126 (Margutti et al., GCN Circ. 8554), covering 100 s of Windowed Timing (WT) and 9.1 ks of Photon Counting (PC) mode data, respectively, between 77 and 24 ks after the trigger. The UVOT-enhanced XRT position was given by Osborne et al. in GCN Circ. 8556. The light-curve can be modelled by a double broken power-law, with an initial decay of alpha_1= 1.2 +/- 0.2, a flat decay of alpha_2= 0.6 +/- 0.1 and a final value of alpha_3= 2.1 +/- 0.2. The two break times are around 200 and 9000 s, respectively. A spectrum extracted from WT data can be modelled with an absorbed power-law, with Gamma = 1.9 +/- 0.2 . A spectrum extracted from PC data in the time interval 3-30 ks post trigger can be modelled with an absorbed power-law, with Gamma = 2.0 +/- 0.1 and a column density of NH = (5.0 +/- 0.7)x10^21 cm^-2, which is compatible with the Galactic value in this direction (4.1x10^21 cm^-2). The observed (unabsorbed) 0.3 -10 keV flux over this time interval is 7.1x10^-12 (1.2x10^-11) erg cm^-2 s^-1. For both spectra there is no strong evidence for intrinsic NH. Uncertainties are given at 90% confidence. If the light-curve continues to decay with alpha ~ 2, the count rate 24 hours after the burst is estimated to be 2.7x10^-3 count s^-1, which corresponds to an observed flux of 1.4x10^-13 erg cm^-2 s^-1. The results of the xrt automatic analysis are available at http://www.swift.ac.uk/xrt_products/00335647. This is an official product of the Swift-XRT team.