TITLE: GCN CIRCULAR NUMBER: 6377 SUBJECT: GRB070506: Swift XRT refined analysis DATE: 07/05/06 17:16:51 GMT FROM: Claudio Pagani at PSU/Swift-XRT C. Pagani, L. Vetere, J. L. Racusin and J. A. Kennea (PSU) report on behalf of the Swift Team: We have analysed the first two orbits of Swift XRT data from GRB 070506 (trigger number 278693, GCN Circ 6375.), for a total photon counting mode exposure of 2.8ks. The XRT started collecting data in Image mode at 05:38:05 UT, 127 seconds after the BAT trigger, but observations in Photon Counting mode were delayed due to the SAA, starting 432 seconds after the trigger. The refined XRT position from 2.8ks of PC data is RA,DEC(J200) = 347.2179, +10.7217 which is RA(J2000) = 23d 08m 52.30s DEC(J200) = +10d 43' 18.2" with an uncertainty of 5.4 arcsec (radius, 90% containment). This is 5.1 arcsec from the initial X-ray position and 2.4 arcsec from the UVOT optical counterpart (GCN 6375). The XRT light curve created from the first two orbits of PC data reveals a decaying source with hints of flaring activity. A power law fit yields a decay slope of 0.55+/-0.06. The X-ray spectrum of the PC data, modeled with an absorbed power law gives a photon index of 2.5+/-0.5 and a total column density of NH= (1.8+/-1.1)e21 cm**-2, in excess of the Galactic value of 0.4e21 cm**-2. The absorbed (unabsorbed) 0.3-10.0keV flux for this spectrum was 3.0E-12 (5.5E-12) ergs cm^-2 s^-1. Assuming the source continues to decay at the same rate, we predict an XRT count rate of 2.2e-2 count/s at T+24 hours, which corresponds to an observed (unabsorbed) flux of 0.8E-12 (1.5E-12) ergs cm^-2 s^-1. This circular is an official product of the Swift XRT team.