GCN Circular 8530
L. Vetere, E. Hoversten (PSU) report on behalf of the Swift-XRT team. The Swift-XRT started observing the field of GRB 081118 (trigger=334877, Hoversten et al., GCN 8525) at 14:59:10.0 UT, 153.3 s after the BAT trigger. The XRT observed the GRB in Windowed Timing (WT) mode until 216 s after the trigger and Photon Counting (PC) mode thereafter. The X-ray light curve from the first three orbits can be modelled with a broken powerlaw with an initial rapid decay (slope of 4.8+/-1.0), a break time of 580 s, followed by a shallower decay (slope of 0.6+/-0.3). The spectrum of the WT data can be well fit by an absorbed powerlaw with a photon index of 2.6 +/- 0.3 and an absorbing equivalent hydrogen column density consistent with the Galactic one in the GRB direction (3.7e20 cm^-2; Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV flux is 1.79 (2.28) x 10^-10 erg cm^-2 s^-1. The PC spectrum (T+250 s to T+19 ks) is best fit with a photon index of 2.5 +/- 0.3 and an absorbing equivalent hydrogen column density consistent with the Galactic one in the GRB direction (3.7e20 cm^-2; Kalberla et al. 2005). The observed (unabsorbed) 0.3-10 keV flux over this interval is 7.6 (9.4) x 10^-13 erg cm^-2 s^-1. Assuming the X-ray emission from the burst continues to decline at the same rate we predict an XRT count rate of 0.002 count s^-1 at T+24 hour, or an observed 0.3-10 keV X-ray flux of 5.2 x 10^-14 erg cm^-2 s^-1. This circular is an official product of the Swift-XRT team.