TITLE: GCN CIRCULAR NUMBER: 7811 SUBJECT: GRB 080603B: Swift-XRT refined analysis DATE: 08/06/04 16:37:24 GMT FROM: Boris Sbarufatti at INAF-IASF-Pa V. Mangano, V. La Parola, B. Sbarufatti (INAF-IASF PA) report on behalf of the Swift-XRT team: The Swift-XRT observed GRB 080603B (trigger 313087, Mangano et al. GCN Circ 7794) for three orbits which consisted of 200 s of Windowed Timing mode data starting 68 s after the trigger and 990 s of Photon Counting mode data, 274 s after the trigger. We obtained a refined XRT position at RA, Dec = 176.53312 68.06058 which is equivalent to: RA (J2000): 11 46 07.95 Dec (J2000): 68 03 38.11 with an uncertainty of 3.7 arcsec (radius, 90% confidence). The position is 3.2 arcsec from the on-board position reported in GCN Circ. 7794 and 0.7 arcsec from the refined UVOT position (Kuin et al. GCN Circ 7808). The X-ray light curve shows an initial steep decay with a slope of 3.4 ± 0.1, breaking to a shallower decay of 0.8 ± 0.1 at a time of 161 ± 6 s after the trigger. A spectrum of the Windowed Timing data can be well fit by an absorbed power-law, with a photon index Gamma = 1.68 ± 0.06 and a column density Nh = (7.9 ± 0.2) e21 cm-2 in excess with respect to the Galactic column density in this direction of 1.2e20 cm-2. The observed (unabsorbed) 0.3-10 keV flux is 7.0e-10 (7.7e-10) erg cm-2 s-1. The Photon Counting mode spectrum is also well fit by an absorbed powerlaw, with an Nh = (1.3 ± 0.2) e22 cm-2 and Gamma = 2.0 ± 0.2. The observed (unabsorbed) 0.3-10 keV flux is 1.55 e-11 (1.91e-11) erg cm-2 s-1. The predicted XRT count rate after 24 hours from burst is 6.0e-2 counts/s This circular is an official product of the Swift-XRT team.