[vsnet-grb-info 1843] GRB 050726: early Swift XRT analysis results

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3683
SUBJECT: GRB 050726: early Swift XRT analysis results
DATE:    05/07/26 16:08:12 GMT
FROM:    Alberto Moretti at Obs Brera Merate  <moretti at merate.mi.astro.it>

A. Moretti (INAF-OAB), S. Campana (INAF-OAB), P. Romano (INAF-OAB), L.A. 
Antonelli (INAF-OAR), M. Chester (PSU), P. Boyd (GSFC-UMBC) on behalf of 
the Swift-XRT Team report.

We have analyzed the Swift XRT data from the first 3 orbit observation 
of  GRB 050726 (Bathelmy et al., GCN 3682). As already reported an 
uncatalogued, fading X-ray source was detected by XRT at the following 
position: RA,Dec 13h 20m 12.30s -32d 03m 50.8s} (J2000) with an 
uncertainty of 6 arcsec (90% containment).
The observations in Windowed Timing (WT) and Photon Counting (PC) mode 
start 132 and 334 seconds from the BAT trigger (T0) respectively.

A preliminary spectral fit (simple absorbed power-law) to the WT data 
yields a photon index of 1.98-/+0.1 in the [0.5-10] keV band. The
derived NH is (1.3)E21 cm^-2, which is higher than the Galactic value  
(0.4E+21 cm-2; Dickey & Lockman 1990). A preliminary spectral fitto the 
PC data yields values well consistent with the WT data.

The light curve shows 2 highly significant flares in the first 200 
seconds and then a monotonic fading which can be fitted with a power law 
of slope 1.06+-0.10

The unabsorbed 0.5-10.0 keV flux at 24 hours after the burst is then 
estimated to be 5E-13 ergs/s/cm2.