TITLE:   GCN CIRCULAR
NUMBER:  7494
SUBJECT: GRB 080320: Swift XRT refined analysis
DATE:    08/03/21 03:33:14 GMT
FROM:    Dirk Grupe at PSU/Swift-XRT  <grupe@astro.psu.edu>

Dirk Grupe reports on behalf of the Swift-XRT team:


The XRT began observing the field of GRB 080320 (trigger=306858; Grupe 
et al.,
GCN Circ 7473) at 04:40:29.4 UT, 171.0 seconds after
the BAT trigger.

The astrometrically corrected X-ray position (using the XRT-UVOT 
alignment and
matching UVOT field sources to the USNO-B1 catalogue) is: RA, Dec = 
177.7353,
+57.1574 which is equivalent to:

RA (J2000):  11 50 56.46
Dec (J2000): +57 09 26.8

with an uncertainty of 1.4 arcsec (radius, 90% confidence).


The 0.3-10 keV X-ray light curve starts with three flares up to 12 
counts/s.
The afterglow decays very fast and started to flatten at the end of the 
first orbit
about 1000 s after the burst. The light curve is currently decaying with a
shallow decay slope of 0.63 +/- 0.05.

The spectrum of the Photon Counting data of the first three orbits
can be well fitted by an absorbed single powerlaw with a photon
index Gamma = 1.96 +/- 0.20 and column density of (6.9 +/- 4.0)e20 cm-2
This is slightly in excess of the Galactic column density of 1.35e20 
cm-2 in this direction.
Using this spectrum we estimated a count rate to flux conversion of
 1 count/s converts to 4.22e-11 ergs/cm2/s.

If the underlying powerlaw decay continues as is, we predict an XRT 
count rate
of 0.026 counts/s at T+24 hours or 1.1e-12 ergs/s/cm2.