TITLE: GCN CIRCULAR NUMBER: 8970 SUBJECT: GRB 090309: Swift-XRT refined analysis DATE: 09/03/10 15:43:56 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team: We have analysed 5.5 ks of XRT data for GRB 090309 (Evans et al. GCN Circ. 8964), from 86 s to 12.4 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN. Circ 8969). The light curve can be modelled with a power-law decay with a decay index of alpha=0.38 (+0.08, -0.09). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 (+/-0.3). The best-fitting absorption column is 2.8 (+1.5, -1.1) x 10^21, in excess of the Galactic value of 1.1 x 10^21 cm^-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1. If the light curve continues to decay with a power-law decay index of 0.38, the count rate at T+24 hours will be 0.012 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.8 x 10^-13 (8.2 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/00345945. This circular is an official product of the Swift-XRT team.