TITLE:   GCN CIRCULAR
NUMBER:  7027
SUBJECT: GRB 071031: Swift-XRT Team refined analysis
DATE:    07/10/31 15:34:32 GMT
FROM:    Michael Stroh at PSU/Swift  <stroh@astroh.org>

M. C. Stroh, A. Falcone and J. L. Racusin (PSU) report on behalf of  
the Swift-XRT Team:

We have analysed the first 4 orbits of Swift-XRT data obtained for GRB  
071031 (Stroh et al. GCN Circ. 7020), totaling 658 s of Windowed  
Timing (WT) data and 7.8ks of Photon Counting (PC) data.

Using 246 s of overlapping XRT Photon Counting mode and UVOT V-band  
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 = 6.40565, -58.05926 which is equivalent to:

RA (J2000): 00 25 37.36
Dec (J2000): -58 03 33.3

with an uncertainty of 2.0 arcsec (radius, 90% confidence). This is  
2.9 and 1.1 arcsec from the previous XRT and UVOT positions  
respectively (Stroh et al., GCN Circ 7020).

The light curve begins with a count rate ~150 cts/s and it is  
dominated by flaring. Two of the flares reach ~200 cts/s while in WT  
mode. By T+10 ks, the flux decreased down to a count rate ~0.01 cts/s.  
Due to the amount of flaring in this X-ray light curve, we are unable  
to determine the slope of the underlying power laws and thus are  
presently unable to predict the count rate at T+24 hours.

The WT data (109-750 seconds) can be modeled as an absorbed power-law,  
with photon index of 1.89 +/- 0.02 and a total absorbing column of NH  
= (7.0 +/- 0.4)e20 cm^-2 which is greater than the Galactic value of  
1.22e20 cm^-2. The 0.3-10 keV absorbed (unabsorbed) flux during this  
time is 1.2e-9 (1.4e-9) erg cm^-2 s^-1.

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