TITLE: GCN CIRCULAR NUMBER: 12235 SUBJECT: GRB 110801A: Swift-XRT refined Analysis DATE: 11/08/02 09:00:16 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester) and M. De Pasquale (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed 9.9 ks of XRT data for GRB 110801A (De Pasquale et al. GCN Circ. 12228), from 89 s to 24.0 ks after the BAT trigger. The data comprise 566 s in Windowed Timing (WT) mode (the first 7 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN. Circ 12232). The light curve initially shows a number of flares, the largest peaking at 500-600 count/s between T+355 s and T+390 s after the trigger. Once this flare has decayed, the light curve after T+800 s can be modelled by a power-law with a slope of 1.12 +/- 0.06. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.754 (+0.025, -0.026). The best-fitting absorption column is 6.4 (+/-0.6) x 10^21 cm^-2, at a redshift of 1.858, in addition to the Galactic value of 6.2 x 10^20 cm^-2 (Kalberla et al. 2005). We note this spectrum includes strong spectral evolution through the flare. The PC mode spectrum has a photon index of 2.04 (+/-0.09) and a best-fitting absorption column of 1.6 (+1.6, -1.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Galactic foreground: 6.2 x 10^20 cm^-2 Intrinsic column: 1.6 (+1.6, -1.4) x 10^21 cm^-2 at z=1.858 Photon index: 2.04 (+/-0.09) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00458521. This circular is an official product of the Swift-XRT team.