[vsnet-grb-info 2113] GRB050908 : Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3952
SUBJECT: GRB050908 : Swift-XRT refined analysis
DATE:    05/09/08 17:41:45 GMT
FROM:    Michael Goad at U Leicester  <mrg at star.le.ac.uk>

M. Goad (UL), K. Page (UL), D. Burrows (PSU) 
report on behalf of the Swift XRT team:

We have analysed the XRT data for GRB050908 (BAT trigger 154112),
between 118s and 24000 s after the trigger. As previously reported
by Goad et al. (GCN3946), there is an uncatalogued fading X-ray source 
in the field of view. The refined coordinates for this burst are

RA(J2000) : 01 21 50.38 
Dec(J2000): -12 57 19.89

with an uncertainty of 6 arcseconds (90% containment). This is 
43 arcseconds from the refined BAT position (GCN3951) and 6 arcseconds
from the position of the candidate optical counterpart (GCN3943).

The initial lightcurve displays 2 large flares with approximately equal
amplitude peaking at T0+145 s and T0+397 s.

The spectrum of the burst in the first orbit of data is well fit by a single
powerlaw with photon index 3.9 +1.1/-0.5 (0.3-10 keV), with evidence for
excess column above the Galactic value of 2.1e20 cm^-2 of NH~3e20 cm^-2.

The spectrum of the burst from T0+4200 to T0+24000 s appears to be harder
with a powerlaw slope of 2.0 +/-0.6.

After the flares the light-curve declines with a slope of -1.33.

If the light-curve continues to decline at this rate the predicted count-rate
at 24 hours after the burst is 5.3e-4 ct s^-1, corresponding to a 0.3-10 keV
unabsorbed flux of 3.3e-14 erg cm^-2 s^-1.