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
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 ). 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.