TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4056
SUBJECT: GRB 051001: Swift XRT refined analysis 
DATE:    05/10/02 10:30:38 GMT
FROM:    Alberto Moretti at Obs Brera Merate  <moretti@merate.mi.astro.it>

A. Moretti (INAF-OAB), P. Romano (INAF-OAB), G. Tagliaferri (INAF-OAB),
S. Campana (INAF-OAB), G. Chincarini (INAF-OAB), 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 day of observation of
GRB 051001 (Moretti et al., GCN  4051). 
As already reported an uncatalogued, fading X-ray source was detected by
XRT. The refined position of the source is 
RA(J2000): 23 23 48.8   
Dec(J2000):-31 31 17.0
We estimate an uncertainty of 6 arcseconds radius (90% containment).

The observations started in Windowed Timing (WT) 192 seconds from the BAT trigger.
The light curve shows a fast decay in the first orbit with a slope of
-2.9+-0.1. Since the second orbit onward the decay 
has been flatter, with a power law slope of -0.65+-0.10.   
The spectral fit (simple absorbed power-law) to the WT data yields a
photon index of 1.48-/+0.02 in the [0.2-10] keV band. The derived NH is
(1.3)E21 cm^-2, which is higher than the Galactic value  (1.4E+20
cm-2; Dickey & Lockman 1990). 

The unabsorbed 0.5-10.0 keV flux of the afterglow at 24 hours after the
burst is then estimated to be 2E-13 ergs/s/cm2.