GCN Circular 4100
A. Beardmore (U. Leicester), D. Burrows, J. Kennea (PSU), N. Gehrels (GSFC) report on behalf of the Swift XRT team: We have analysed the first two orbits of data from the Swift XRT observation of GRB051016 (Boyd et al., GCN4096). The refined ground processed coordinates are : RA(J2000) = 08h 11m 16.3s Dec(J2000) = -18d 17m 56.3s with an estimated uncertainty of 8 arcsecs radius (90% containment). This is 7.1 arcsecs awsy from the XRT position reported in Boyd et al. The XRT light curve from this interval shows a steep initial decline, followed by a break to a shallower decay slope. A broken power-law fit to the light curve gives parameters : alpha_1 = 4.8 +0.5-0.4 t_break = 247 +/- 15s alpha_2 = 0.7 +/- 0.1. The Windowed Timing (WT) and Photon Counting mode spectra from the first two orbits can be fit with an absorbed power-law with a photon index of 3.14+/-0.45 and a column density of 4.5+/-1.5 E21 cm-2, which is slightly in excess of the Galactic column density of 1.19E+21 cm-2 in this direction. The observed 0.2-10 keV flux for the WT data (exposure time 22.2s, centered at T+130s) was 1.31E-10 ergs cm**-2 s**-1, corresponding to an unabsorbed flux of 9.98E-10 ergs cm**-2 s**-1. Assuming the X-ray emission from the GRB continues to decline at the same rate, the predicted XRT count rate at T+24hrs is 0.0036 counts/s, which corresponds to an observed 0.2-10 keV flux of 1.1e-13 ergs cm**-2 s**-1.