TITLE: GCN CIRCULAR NUMBER: 6118 SUBJECT: GRB 070220: Swift-XRT Refined Analysis DATE: 07/02/20 13:04:43 GMT FROM: Andy Beardmore at U Leicester A.P. Beardmore (U. Leicester), M. Stamatikos (NASA/ORAU), P.A. Evans, M.R. Goad, O. Godet, K.L. Page, (U. Leicester), M. Capalbi (ASDC), J.P. Osborne, R.L.C. Starling (U. Leicester) report on behalf of the Swift-XRT team: We have analysed the first two orbits of Swift-XRT data available for GRB 070220 (Stamatikos et al., GCN 6114), which were obtained prior to the satellite entering the Malindi Gap. The data consist of 217s exposure in Windowed Timing (WT) mode and 4090s in Photon Counting (PC) mode. Using the PC data, we find a refined XRT position, which has been astrometrically corrected by matching the UVOT images with the USNO-B1 catalogue, of: RA(J2000) = 02h 19m 06.83s DEC(J2000) = +68d 48' 16.1" with an uncertainty of 2.0 arcseconds (90% confidence). This position is 72.0 arcseconds and 3.0 arcseconds away from the original BAT and XRT positions quoted in GCN 6114. The 0.3-10.0 keV X-ray light curve out to T+7.6ks (where T is the BAT trigger time) can be fit by a broken powerlaw, with an initial decay slope of 1.76+/-0.06, a break time of 417+/-43s, and a post-break slope of 0.99+/-0.04. The WT spectrum from T+85s to T+294s can be modelled by an absorbed powerlaw, with a photon index of 1.55+/-0.08 and a column density of (4.9+/-0.5)e21 cm^-2 (compared with the Galactic value in this direction of 3.8e21 cm^-2). The 0.3-10.0 keV observed flux over this time interval is (1.21+/-0.05)e-9 ergs cm^-2 s^-1, which corresponds to an unabsorbed flux of (1.65+/-0.10)e-9 ergs cm^-2 s^-1. While the temporal decay parameters are uncertain based on such limited data, assuming the source continues to fade at the same rate we predict an X-ray count rate of 0.019 count/s at T+24 hours, which corresponds to an observed (unabsorbed) 0.3-10.0 keV flux of 1.4e-12 (1.9e-12) ergs cm^2 s^-1. This circular is an official product of the Swift-XRT team.