[vsnet-grb-info 1892] GCN 050801: early Swift XRT analysis results

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3731
SUBJECT: GCN 050801: early Swift XRT analysis results
DATE:    05/08/02 04:38:24 GMT
FROM:    Matteo Perri at ISAC/ASDC  <perri at asdc.asi.it>

M. Perri, M. Capalbi, P. Giommi (ASDC), J. Kennea, D.N. Burrows, P.
Meszaros
(PSU), K. Hinshaw (GSFC-SPSYS) report on behalf of the Swift XRT team:


We have analyzed the Swift XRT data from the first orbit observation
of GRB 050801 (Band et al., GCN 3725). A fading, previously uncatalogued,
point source at the following coordinates is detected in the field:

RA(J2000) = 13h 36m 36.0s
Dec(J2000) = -21d 55' 42"

This position is 83 arcseconds from the BAT position given in GCN
3725 (Band et al.) and 8.5 arcsec from the ROTSE-III position reported
in GCN 3723 (Rykoff et al.). The source is close to a bad column of the
CCD
and we estimate an uncertainty of 10 arcseconds radius in the derived
position.

Data in Photon Counting (PC) mode starts at 18:29:31 UT, 89 seconds from
the BAT trigger. The 0.3-10 keV afterglow light curve shows a flat slope
from T+89s to T+300s and then declines following a power law with decay
index
alpha=-1.3+/-0.3 up to T+990s, when first orbits ends.

A preliminary spectral fit in the 0.3-10 keV energy band to the first
orbit
gives a spectral power law photon index of 1.8+/-0.3 with Nh=5.7E20 cm^-2.

In the time range 89-990 seconds from trigger the average unabsorbed
0.5-10 keV flux is 2.6E-11 erg cm^-2 s^-1.