[vsnet-grb-info 2483] GRB 051210: Swift XRT refined analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4320
SUBJECT: GRB 051210: Swift XRT refined analysis
DATE:    05/12/10 13:35:32 GMT
FROM:    David Burrows at PSU/Swift  <dxb15 at psu.edu>

V. Mangano, G. Cusumano, V. La Parola (INAF-IASF), D. N. Burrows (PSU), L. 
Angelini (GSFC-JHU), and N. White (GSFC) report on behalf of the Swift team:


We have analyzed the Swift XRT data from the first observation
of GRB 051210 (Mangano et al. 2005, GCN 4315) consisting
of three orbits (about 5.7 ks exposure).
The refined coordinates of the X-ray afterglow are:

RA(J2000)  = +22h 00m 41.3s
Dec(J2000) = -57d 36' 48.2"

with an estimated uncertainty of 4.2 arcseconds radius (90%
containment). The XRT boresight correction has been applied
through the new TELDEF file provided by the Swift Science
Data Center (Angelini et al. 2005, GCN 4313).
This position is 54.4 arcsec from the revised BAT position given
in GCN 4318 (Sato et al. 2005) and 3 arcsec from
the XRT position determined on board (Mangano et al. 2005, GCN 4315).

The 0.2-10 keV light curve, that starts in Windowed Timing (WT) mode
87.3 seconds after the BAT trigger, shows a fading behaviour with
a decaying slope of 2.3+/-0.1 over the first two orbits and
is not detectable anymore during the third (the expected count rate
at the end of the third orbit would be 7.0e-4 c/s).

A preliminary spectral fit to WT and PC data of the first two orbits
with an absorbed power law gives a photon index of 1.5+/-0.1 and an
absorption column of (7.5 +/- 3) x 1e20 cm^-2.
The Galactic absorption in the GRB direction is 2.2e20 cm^-2.
Assuming the current steep decay we predict a flux lower than
1.e-16 erg cm^-2 s^-1 at one day from the burst.