TITLE: GCN CIRCULAR NUMBER: 3602 SUBJECT: GRB050713b: XRT refined analysis DATE: 05/07/13 21:37:29 GMT FROM: David Burrows at PSU/Swift K. Page, S. Vaughan, M. Goad (Leicester), D. N. Burrows (PSU), M. Ajello (MPE), R. Fink and N. Gehrels (GSFC) report on behalf of the Swift XRT team: We have analysed the first two orbits of data for GRB050713b (GCN 3590, Vaughan et al., 2005). Using xrtcentoid, the refined position is: RA(J2000) = 20h 31m 15.5s Dec(J2000) = +60d 56' 40.4" with an uncertainty of 6 arcsec. This is only 2 arcsec from the original XRT position (GCN 3590, Vaughan et al., 2005). The light-curve shows a steeply fading afterglow during the first orbit, with a decay slope of alpha = 2.88 +/- 0.12 between 143 and 600 seconds after the trigger. After ~5000 seconds (i.e. on the second orbit), the light-curve flattens significantly; more data are required to constrain the slope following the break in the light curve. The WT spectrum can be fitted by an absorbed power-law with a spectral index, Gamma = 1.70 +0.11/-0.09 and excess NH of (1.97 +0.50/-0.43)e21 cm^-2. The unabsorbed 0.3-10 keV flux (averaged over 143 and 330 seconds after the burst) is (9.02 +0.16/0.80)e-10 erg cm^-2 s^-1.