TITLE: GCN CIRCULAR NUMBER: 7674 SUBJECT: GRB080503 XRT refined analysis DATE: 08/05/03 22:52:44 GMT FROM: Jirong Mao at INAF-OAB GRB 080503: Swift-XRT refined analysis C. Guidorzi & J. Mao (INAF-OAB) report on behalf of the Swift-XRT team: The Swift-XRT began observing GRB 080503 (trigger=310785, Mao et al., GCN Circ. 7665) in Window Timing mode, 81 s after the BAT trigger. The enhanced XRT position was given in Goad et al. (GCN Circ. 7669). The light curve from 81 s to 13.2 ks can be modelled with the combination of an exponential with a power law taking over at late time, with the following best-fitting parameters: e-folding time= (72 ± 4) s, power-law index alpha= 2.2 (-1.1, +0.6). The chisq/dof=202/151 is due to short-term variability superposed to the model. The WT mode spectrum spanning from 81 to 282 s can be fit by a power-law model, with a photon index of 1.27 ± 0.03 and column density consistent with the average Galactic column density in this direction of 5.6e20 cm^-2. The PC mode spectrum, starting from 282 s and totalling 6.3 ks of exposure, is fit with a power law with a photon index of 2.45+/-0.25 and no evidence for any additional column density with respect to the Galactic one. The corresponding observed (unabsorbed) 0.3-10 keV flux is 2.9e-12 (3.9e-12) erg cm^-2 s^-1. If the burst continues to decay at the same rate, we predict an XRT count rate of 1.7e-6 count/s at T+24 hours, which corresponds to an observed 0.3-10 keV flux of approximately 4e-17 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team.