TITLE: GCN CIRCULAR NUMBER: 7153 SUBJECT: GRB 071227: Swift-XRT refined analysis DATE: 07/12/28 10:41:36 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore, K.L. Page (U. Leicester) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift-XRT team: The Swift-XRT began observing GRB 071227 (trigger #299787) at 20:15:04UT, 79.5 seconds after the BAT trigger (Sakamoto et al., GCN Circ. 7147). Using 382 s of overlapping XRT Photon Counting mode and UVOT V-band data, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) of RA, Dec = 58.13002, -55.98419, which is equivalent to: RA (J2000): 03h 52m 31.21s Dec (J2000): -55d 59' 03.1" with an uncertainty of 2.0 arcsec (radius, 90% confidence). This is 4.5 arcsec away from the position derived from the promptly downlinked XRT data reported in Sakamoto et al. (GCN Circ. 7147), 91 arcsec from the refined BAT position of Sato et al. (GCN Circ. 7148) and 2.6 arcsec from the possible UVOT optical transient reported by Cucchiara and Sakamoto (GCN Circ. 7150). The XRT light curve from 210s to 34.8ks after the BAT trigger can be modelled by a doubly broken power-law, with parameters alpha1 = 1.1 +/- 0.2, tbreak1 = 183 +/- 7s, alpha2 = 5.3 +1.2 -0.6, tbreak2 = 389 +/- 65s, alpha3 = 1.1 +/- 0.2. The XRT spectrum from a time interval spanning 104s to 208s after the BAT trigger is well fit by an absorbed power-law, with a photon index of 1.62+/-0.14 and a column density (9.3+/-4.3)e20 cm^-2, in addition to the Galactic column of 2.6e20 cm^-2 in this direction. The observed (unabsorbed) 0.3-10.0 keV flux from this period is 3.9e-10 (4.6e-10) ergs cm^-2 s^-1. The predicted XRT count rate 24 hours after the trigger is 4.0e-4 count s^-1, which corresponds to an observed 0.3-10.0 keV flux of 2.0e-14 ergs cm^-2 s^-1. This circular is an official product of the Swift-XRT team.