TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3519 SUBJECT: GRB 050603 - XRT data analysis of the first day DATE: 05/06/05 17:25:30 GMT FROM: Dirk Grupe at PSU/Swift-XRT subject: GRB 050603 - XRT data analysis of the first day D. Grupe, A. Retter, D. Burrows, J. Kennea (PSU), and N Gehrels (GSFC), on behalf of the Swift XRT team report: We analyzed the XRT data of the first day of observation of the GRB 050603 (Retter et al., GCN #3509). The observations started approximately 11 hours after the burst (Racusin et al., GCN #3514). Preliminary analysis of the data obtained so far (31 ks) give the following refined coordinates: Ra-2000: 02h 39m 56.8s Dec-2000: -25d 10' 59.8" The centroiding error is 6". This position is about 7" off the X-ray position given in Racusin et al. (GCN #3514) and 5" off the radio position (Cameron, GCN #3113) and the UVOT position given in Brown et al. (GCN #3116). The source had a flux of 2.2e-12 ergs/s/cm2 11 hours after the burst and is decaying with a decay slope alpha=1.78+/-0.14. The X-ray spectrum can be fitted with a single powerlaw with an X-ray spectral slope beta=0.80+/-0.08. The fit is consistent with Galactic absorption (NH=2e20 1/cm2). This message may be cited