GCN Circular 8705

Dirk Grupe (PSU) reports on behalf of the Swift-XRT team:


The XRT began observing the field of GRB 081222 (trigger=337914; Grupe et al.,
GCN Circ 8691) on 2008-December-22 at 04:54:51.7 UT, 51.8 seconds after
the BAT trigger.


The 0.3-10 keV X-ray light curve of the first five orbits
displays a smooth light curve that can be fitted with an initial decay slope
alpha1 = 0.90+/-0.02 with a break at 1420+/-100s followed by a steeper decay
slope alpha2=1.20+/-0.02.

The spectrum of the Windowed Timing data of the first orbit
can be well fitted by an absorbed single
power law model with a photon
index Gamma = 2.01 +/- 0.20 and a column density
NH=(4.61+/-0.80)e20 which is in excess of the Galactic column density in the
direction of the burst of NH-gal=2.24e20 (Kalberla et al. 2005).
The photon counting mode data of the first five orbits are consistent 
with this
result.


If the underlying power law decay of 1.2
continues as is, we predict an XRT count rate
of 0.030 counts/s at T+24 hours or 1e-12 ergs/s/cm2 and at T+48 hours 0.015
counts/s or 5e-13 ergs/s/cm2.

This circular is an official product of the Swift-XRT team.

[GCN OPS NOTE(23dec08):  Per author's request, the "081221" in the first line
was changed to "081222".]