TITLE: GCN CIRCULAR NUMBER: 10125 SUBJECT: GRB 091102: Swift-XRT refined analysis DATE: 09/11/03 06:23:30 GMT FROM: Loredana Vetere at PSU L. Vetere and E. A. Hoversten (PSU) report on behalf of the Swift-XRT team: We have analysed 1.4 ks of XRT data for GRB 091102 (Hoversten et al. GCN Circ. 10117), from 988 s to 19 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. The enhanced XRT position has already been determined by Kennea et al. (GCN Circ. 10120). The PC light curve shows a steep drop at 1.3 ks after the BAT trigger with a decay index of alpha=2.9 +/- 0.6. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.0 (+0.8, -0.6). The best-fitting absorption column is 2.4 (+2.5, -1.3) x 10^21 cm^-2, consistent with 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 4.2 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00374598. This circular is an official product of the Swift-XRT team.