GCN Circular 5554

P.A. Evans, A.P. Beardmore, O. Godet and K.L. Page (U. Leicester) report on
behalf of the Swift/XRT team:

We have analysed the first 2 orbits of Swift data of GRB 060908 (Evans et al.,
GCN 5544
Not found
 
 
), totalling 100 s of data in Window Timing mode (WT) and 2.5 ks in 
Photon Counting mode (PC).

The PC mode image provides a refined XRT position of

RA(J2000)   =  02 07 18.21
Dec(J2000)  = +00 20 28.8

with an error of 3.6" (90% confidence). This position is within 1.5" of the
initial XRT position, and 3.4" from the UVOT position, reported in GCN 5554
Not found
 
 
.

Spectral fits to the first orbit of data suggest an absorption column in excess
of the Galactic value (2.4e20 cm^-2). The WT data yielded 8.0+4.9/-4.0 e20 cm^-2
and the PC mode data gave 6.4+3.4/-3.0 e20 cm^-2.

There is also evidence for spectral evolution during the first orbit: the WT
mode photon index was 2.43 (+0.30, -0.26), while the PC mode photon index was
1.95 (+0.15,-0.14). The observed PC mode flux was 7.5e-11 erg/s/cm^2 during the
first orbit; which translates to an unabsorbed flux of 8.9e-11 erg/s/cm^2

The lightcurve of the first 2 orbits (T0+78 to T0+6600) can be modelled with
a single power-law, and a flare at around 800s. The decay slope is 1.11
+/-0.06, and we thus predict a count rate of 0.004 counts per second 24 hours
after the trigger. This translates to a flux of 1.56e-13 erg/s/cm^2, or an
unabsorbed flux of 1.85e-13 erg/s/cm^2.

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

-- 
-------------------------

Phil Evans,
PDRA/Swift Scientist
X-ray and Observational Astronomy Group,
University of Leicester

Tel: (0116) 252 5059
pae9@star.le.ac.uk
http://www.astro.keele.ac.uk/~pae