GCN Circular 5444

A. Moretti (INAF-OAB), C. Guidorzi (Univ. Bicocca & INAF-OAB),
P. Romano (INAF-OAB) report on behalf of the Swift-XRT team:

We have analysed the first 4 orbits of Swift-XRT data obtained for GRB
060813 (trigger number 224364). The data consist of 611 s in Windowed
Timing (WT) mode, starting 76 seconds after the BAT trigger and 7 ks
in Photon Counting (PC) mode.  Using PC data we obtain a refined
position of:

RA(J2000) =   07 27 35.36
Dec(J2000) = -29 50 54.2

with an estimated uncertainty radius of 3.5 arcsec (90% containment).
This is at 27" from the refined BAT position (Cummings et al., GCN
Circ. 5443
Loading...
 
 ).

The light-curve shows a shallow decay with alpha = 0.58+/- 0.05, in
the first part up to a break at time=861+/-180 s. After the break
data show a decline with alpha = 1.10+/- 0.05.

The spectrum formed from all the WT data before the light-curve break
can be modelled with a power-law of photon index Gamma = 1.98 +/-
0.08, with an absorbing column of NH = (4.4 +/- 0.4)e21 cm^-2
marginally consistent with the Galactic value of 3.1e21 cm^-2.
The spectrum formed from the PC data after the light-curve break is
maginally consistent with the pre-break spectrum: it can be modelled
with a power-law of photon index Gamma = 1.80 +/- 0.10, with an
absorbing column of NH = (3.2 +/- 0.5)e21 cm^-2.

Assuming the light-curve continues to decay with alpha ~ 1.10, the
count rate at 24 hours is predicted to be 0.023 count s^-1. This
corresponds to an observed (unabsorbed) flux of 1.4e-12 (1.9e-12)
erg cm^-2 s^-1.

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