TITLE: GCN CIRCULAR NUMBER: 6167 SUBJECT: GRB070227: Swift-XRT refined analysis DATE: 07/03/05 21:07:47 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani, J. L. Racusin, L. Vetere, D. Grupe, D. N. Burrows (PSU), report on behalf of the Swift XRT team: We have analysed the Swift-XRT Photon Counting data of GRB 070227 (GCN Circ. 6156) from T+56ks to T+386ks (where T is the BAT trigger time). The candidate X-ray afterglow reported in GCN Circ. 6157 has faded from the initial count rate of ~ 0.01 counts/s to a count rate of 0.002 counts/s. Using 39ks of PC data the refined XRT position is RA,Dec= 120.5805, -46.3135 which is: RA(J2000): 08h 02m 19.33s Dec(J2000): -46d 18' 48.7" with an uncertainty of 4 arcseconds (90% containment). This position is 47 arcseconds from the refined BAT position given in GCN Circ. 6158 and 0.7 arcseconds from the XRT position given in GCN Circ. 6157. The light-curve shows an initial flat phase during the first 20ks of XRT obervations ending at about 80ks after the burst, followed by a decay that can be fitted with a power law with index 0.9+/-0.2. The spectral fit to the PC data is not very well constrained due to the low number of afterglow events. The fit with an absorbed power law, applying C-statistics, gives a photon index of 2.9 (+0.8/-0.5) in the [0.3-10] keV band, and a column density of (0.57 +0.26/-0.18)e22 cm^-2 (compared with the Galactic value in this direction of 0.31e22 cm^-2). The average estimated unabsorbed 0.3-10 keV flux from T+56ks to T+386ks of XRT Photon Counting observations was 3.6e-13 erg cm^-2 s^-1. This Circular is an official product of the Swift XRT Team.