[vsnet-grb-info 6156] GRB 080602: Swift-XRT refined analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7785
SUBJECT: GRB 080602: Swift-XRT refined analysis
DATE:    08/06/02 20:03:58 GMT
FROM:    Andy Beardmore at U Leicester  <apb at star.le.ac.uk>

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

The Swift-XRT observed GRB 080602 (trigger 312958, Beardmore et
al. GCN 7781) for one orbit which consisted of 71 s of Windowed
Timing mode data starting 118 s after the trigger and 1.23 ks  of
Photon Counting mode data, 193 s after the trigger.

Using 930 s of overlapping XRT Photon Counting mode and UVOT data, we
find an astrometrically corrected X-ray position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 19.17574, -9.23207 which is equivalent to:

RA (J2000): 01 16 42.18
Dec (J2000): -09 13 55.4

with an uncertainty of 1.7 arcsec (radius, 90% confidence). The position 
is 6.3 arcsec from the on-board position reported in GCN 7781 and 0.4 
arcsec from the initial refined XRT position reported in GCN 7782.

At first, the X-ray light curve shows signs of a steep decay with a slope 
of 4.7 +2.1/-0.9, breaking to a shallower decay of 0.21 +/- 0.16 at 
a time of 145 +11/-6 s after the trigger. This is followed by a further 
steepening  to a slope of 0.76 +0.41/-0.23 at a time of 561 +276/-201 s.

A spectrum of the Windowed Timing data can be well fit by an absorbed
power-law, with a photon index Gamma = 1.63 +/- 0.21 and a column
density Nh = (1.0 +/- 0.5) e21 cm^-2, compared with the Galactic
column density in this direction of 3.5e20 cm^-2. The observed
(unabsorbed) 0.3-10 keV flux is 3.13e-10 (3.61e-10) erg cm^-2 s^-1.

The Photon Counting mode spectrum is also well fit by an absorbed
powerlaw, with Nh = (2.1 +/- 0.4) e21 cm^-2 and Gamma = 2.12 +/- 0.15.
The observed (unabsorbed) 0.3-10 keV flux is 1.66 e-10 (2.59e-10)
erg cm^-2 s^-1.  The observed count to flux conversion factor for this
data is 3.5e-11 erg cm^-2 count^-1.

Due to the limited XRT data available, no count rate prediction at T+1 day
has been made. No further observations with Swift are planned.

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