TITLE: GCN CIRCULAR NUMBER: 9378 SUBJECT: GRB 090516: Swift XRT refined analysis DATE: 09/05/16 20:04:01 GMT FROM: Antonia Rowlinson at U.of Leicester B. A. Rowlinson and P. Evans (U Leicester) report on behalf of the Swift-XRT team: We have analysed 3.0 ks of XRT data for GRB 090516 (Rowlinson et al. GCN Circ. 9374), from 170 s to 6.4 ks after the BAT trigger. The data comprise 327 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN. Circ 9376). The light curve can be modelled with a power-law decay with two flares superimposed on it. The initial decay index is alpha=3.27 (+0.11, -0.10). At T+601 (+138, -52) s the decay flattens to an alpha of 0.93 (+0.11, -0.10). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.09 (+/-0.04). The best-fitting absorption column is 1.57 (+0.10, -0.09) x 10^21 cm^-2, in excess of the Galactic value of 4.5 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index of 2.09 (+0.13, -0.12) and a best-fitting absorption column of 9.6 (+2.6, -2.5) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 0.93, the count rate at T+24 hours will be 0.03 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x 10^-12 (1.4 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/00352190. This circular is an official product of the Swift-XRT team.