TITLE: GCN CIRCULAR NUMBER: 8543 SUBJECT: GRB 081121: Swift-XRT refined analysis DATE: 08/11/22 11:43:57 GMT FROM: Olivier Godet at U.of Leicester O. Godet (U Leicester) and S. Oates (UCL-MSSL) on behalf the Swift-XRT team: The Swift-XRT started observing the field of GRB 081121 (trigger number 335105, Oates et al., GCN Circ. 8537) at 2008-11-21 20:35:32 UT, 2.8 ks after the trigger. The best XRT position is the UVOT-enhanced position reported by Goad et al. (GCN Circ. 8541). This position is consistent with the optical positions reported by the Swift-UVOT and ROTSE III (Oates et al., GCN Circ. 8538; Yuan et al., GCN Circ. 8536). The X-ray light curve presently spans 4.2 ks of photon counting (PC) mode data from T+2.8 ks to T+16 ks. The light curve shows an initial decay with a slope of 1.11 +0.06/-0.05 up to at least ~T+17 ks, followed by a steep decay up to ~T+20 ks and then a flatter decay with a slope of 0.25 +0.62/-0.13. The PC X-ray spectrum from the same interval can be well fit by an absorbed power-law with a photon index of 1.99 +0.10/-0.09 and a column density of (9.7 +2.2/-2.0) x 10^20 cm^-2 (the Galactic value is 4.0 x 10^20 cm^-2 in the direction of the burst). The observed 0.3-10.0 keV flux is (7.1 +/-0.4) x 10^-11 erg cm^-2 s^-1 which corresponds to an unabsorbed flux of (9.0 +0.2/-0.5) x 10^-11 erg cm^-2 s^-1. If the burst continues on the current plateau phase, the predicted count rate at T+1 day would be approximately 1.2 x 10^-1 count s^-1. This is an official product of the Swift-XRT team.