TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4205 SUBJECT: GRB051028: Swift-XRT refined analysis DATE: 05/11/07 12:03:55 GMT FROM: Kim Page at U.of Leicester K.L. Page, M.R. Goad (U. Leicester), D.N. Burrows, J. Racusin (PSU), S. Oates (MSSL), M. Ajello (MPE) and M. Trippico (GSFC-SSAI) report on behalf of the Swift XRT team: We have analysed 38 ks of XRT observations of the HETE burst GRB051028 (trigger number H3951; GCN 4172, Hurley et al.), between approximately 7.1 and 178 hours after the trigger. As reported in GCN 4174 (Racusin et al.), there is an uncatalogued, fading X-ray source within the HETE error circle. The refined coordinates for this X-ray afterglow are: RA(J2000): 01 48 15.1 Dec(J2000): +47 45 12.9 with an estimated uncertainty of 3.8 arcsec (90% containment) and including the latest XRT boresight correction. The position is 0.6 arcsec from that given by Racusin et al. (GCN 4174) and 3.9 arcsec from the optical afterglow detected by the WHT (GCNs 4175, Jelinek et al., and 4176, Pandey et al.) The X-ray light-curve shows a simple power-law decay with a slope of 1.25 +0.25/-0.16. The spectrum of the full 38 ks of data can also be modelled with a power-law, with photon index, Gamma = 1.74 +/- 0.21. There is no evidence for an absorbing column higher than the Galactic value of 1.2e21 cm^-2. At 7.1 hours, the 0.3-10 keV observed (unabsorbed) flux was ~1.8e-12 (2.2e-12) erg cm^-2 s^-1. At 178 hours, the afterglow had faded to an observed (unabsorbed) flux level of 2.3e-14 (2.8e-14) erg cm^-2 s^-1.