TITLE: GCN CIRCULAR NUMBER: 10503 SUBJECT: GRB 100316A: Swift-XRT refined analysis DATE: 10/03/16 17:21:12 GMT FROM: Andy Beardmore at U Leicester A. P. Beardmore (U. Leicester) and W. H. Baumgartner (GSFC/UMBC) report on behalf of the Swift-XRT team: Due to an Earth-limb constraint, Swift performed a delayed slew to GRB 100316A (Baumgartner et al. GCN Circ. 10484), with XRT observations starting 3.2 ks after the BAT trigger. The enhanced XRT position for this burst was given by Evans (GCN. Circ 10490). The X-ray light curve, obtained from 7.5 ks of Photon Counting (PC) mode data spanning 3.2 ks to 17.3 ks after the trigger, can be modelled by a power-law decay, with a decay slope of 1.3 +/- 0.3. An X-ray spectrum formed from the same data can be modelled by an absorbed power-law, with a photon index of 2.3 +0.3 -0.5 and absorbing column density of (1.5 +1.2 -1.1) x 10^21 cm^-2, which is in excess of the Galactic value of 4.4 x 10^20 cm^-2 (Kalberla et al. 2005) in the direction of the source. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.4 x 10^-11 (5.3 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay at the same rate, the count rate at T+24 hours will be 1.2 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.0 x 10^-14 (6.3 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00416076. This circular is an official product of the Swift-XRT team.