TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5227 SUBJECT: GRB 060605: Swift-XRT Team refined analysis DATE: 06/06/06 11:30:05 GMT FROM: Olivier Godet at U.of Leicester O. Godet, K.L. Page, E. Rol, A.P. Beardmore (U. Leicester), M.J. Page (UCL-MSSL) report on behalf of the Swift-XRT team: We have analysed the first 5 orbits of X-ray data obtained for GRB 060605 (BAT trigger 213630). Using 10.4 ks of Photon Counting (PC) mode data, we find a refined position of: RA(J2000) = 21h 28m 37.16s Dec(J2000) = -06d 03' 33.8" with an uncertainty of 3.6 arcsec (90% containment). This is 0.7 and 2.7 arcsec from the on-board XRT and UVOT positions respectively and 38.8 arcsec from the on-board BAT position given in GCN 5221 by Page et al. The source was relatively faint in the XRT. The light-curve shows the common steep-to-flat-to-steep transition: i) for the first steep segment, alpha_1 = 2.34 +/-0.55 followed by a break at t1 = 171 +/-26s after the BAT trigger (T0); for the shallow decay, alpha_2 = 0.38 +0.05/-0.06 followed by another break at t2 = T0+5508 + 2029/-904s; iii) alpha_3 = 1.23 +0.73/-0.23. The first orbit of the WT data (from T0+99s to T0+124s) is well fitted by a single power-law with Gamma = 1.6 +0.42/-0.39, with no strong evidence for excess NH above the Galactic value of 5.1e20 cm^-2. The spectrum of the PC data from T0+126s to T0+2.4e4s is well fitted by a single power-law with Gamma = 1.97 +/-0.06, again with no strong evidence for excess NH above the Galactic value of 5.1e20 cm^-2. The unabsorbed flux in the 0.3-10 keV energy band is 7.5 +0.7/-0.6 e-12 erg cm^-2 s^-1. No significant spectral evolution is seen before and after the second break at t2. We note that Khamitov et al. (GCN 5224) claimed for a break in optical between T0+1 and T0+5 hours, which could be consistent with the second break at t2 seen in the XRT light-curve. Assuming the decay continues to follow the temporal slope alpha_3, the predicted count rate at T0+24 hours is 0.010 count s^-1, corresponding to an observed (unabsorbed) flux of 4.46e-13 (5.13e-12) erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team.