TITLE:   GCN CIRCULAR
NUMBER:  6363
SUBJECT: GRB 070429A: Swift XRT refined analysis
DATE:    07/04/29 16:11:08 GMT
FROM:    Rhaana Starling at U of Leicester  <rlcs1@star.le.ac.uk>

R.L.C. Starling, A.P. Beardmore, K.L. Page, P.A. Evans (U. Leicester) and 
J. Cannizzo (GSFC/UMBC) report on behalf of the Swift XRT team:

We have analysed Swift XRT data from the first orbit of Windowed Timing
mode and two subsequent orbits in Photon Counting (PC) mode for GRB
070429A (trigger 277571, Barthelmy et al. GCN Circ 6355).

Using 380s of overlapping XRT PC mode data and UVOT V-band data, we
obtain an astrometrically corrected (using the USNO-B1 catalogue) X-ray
position of RA, Dec (J2000) = 297.70333, -32.40497, which is
RA(J2000) =   19h 50m 48.80s
Dec(J2000) = -32d 24' 17.9"
with an estimated uncertainty of 2.4 arcsec (90% error radius).
This is 1.0 arcsec from the XRT position in GCN 6355 and
1.6 arcsec from the possible K-band optical transient report by
de Ugarte Postigo et al. (GCN Circ 6361).

The lightcurve is well fitted by a broken power law with
alpha1=6.4+0.3/-0.4, Tbreak=235+2/-20 s and alpha2=3.2+0.3/-0.2.

The PC mode spectrum can be fit with a single absorbed power law. The
photon index is 1.8+0.4/-0.2 and the
absorption is centred at 1.3E21 cm^-2 but is poorly constrained. The
Galactic column towards this position is 0.9E21 cm^-2.
The 0.3-10 keV flux is 1.25E-11 erg/cm^2/s, corresponding to 0.11
cts/s.

We are now in a data gap for this source, whilst Swift is
observing GRB 070429B, so the current decay rate
is not known, hence we do not give a predicted count rate for 24hr.
Further Swift observations of this source are planned.

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