GCN Circular 6056

O. Godet, K. Page, P. Evans, J. Osborne (U. Leicester), D. N. Burrows
(PSU) report on behalf of the Swift XRT team:

We analysed the first 5 orbits of XRT data from GRB 070129 (from T0+140s
to T0+24749s).  An 11ks photon counting (PC) mode image provides a
refined XRT position:

RA(J2000) = 02h 28m 00.83s
Dec(J2000) = +11d 41' 05.1''

with an uncertainty of 3.6 arcsec (90% containment). This position is
within the BAT error circle and is 2.5 arcsec away from the on-board XRT
position quoted in Godet et al. (GCN 6053
Not found
 
 
) and includes the latest XRT
boresight correction. We note that our error circle includes the
position of the source reported in Malesani et al. 2007 (GCN 070129
Not found
 
 
). 

The BAT triggered on a precursor and saw the main burst around T0+380s.
The XRT started to observe the field 140s after the BAT trigger (T0).
The X-ray light curve shows the main burst consisting of several X-ray
flares from T0+140s to T0+700s, followed by a steep decay to T0+1200s
and then a flatter decay (so far to T0+24749s). This flatter decay can
be fitted by a single power-law with a decay slope of alpha = 0.33
+0.09/-0.10.

The Windowed Timing (WT) data correspond to the main burst, which shows
strong spectral evolution.  An absorbed power-law fit of the WT data
(first orbit) from T+140s to T+792s gives a photon index of 1.81+/-0.03
and an absorption value of (2.1 +/-0.1)e21 cm**-2, compared to the
Galactic value of 8.4e20 cm**-2 in the burst direction.  The error are
given at a 90% confidence level.  The spectrum of the PC data from T0
+795s to T0+24749s can be fit by an absorbed power-law with Gamma = 2.39
+0.22/-0.19 and an absorption value of (1.6 +/-0.5)e21 cm**-2.

If the burst continues decaying at the current rate (alpha = 0.33) we
estimate an XRT count rate of 0.042 counts/s at T0 + 24hr, which
corresponds to an observed 0.3-10.keV flux of 2.5e-12 ergs cm**-2 s**-1
and an unabsorbed flux of 2.9e-12 ergs cm**-2 s**-1.

This circular is an official product of the Swift XRT Team.