[vsnet-grb-info 3720] GRB 060908, Swift/XRT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5554
SUBJECT: GRB 060908, Swift/XRT refined analysis
DATE:    06/09/08 15:29:25 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at star.le.ac.uk>

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), 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.

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 at star.le.ac.uk
http://www.astro.keele.ac.uk/~pae