[vsnet-grb-info 12253] GRB 120805A: Enhanced Swift-XRT position

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13638
SUBJECT: GRB 120805A: Enhanced Swift-XRT position
DATE:    12/08/14 08:26:46 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

We have reinvestigated the XRT position of GRB 120805A. Using 2.6 ks of
XRT Photon Counting mode data and 2 UVOT images, 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 =
216.53836, 5.82525 which is equivalent to:

RA (J2000):  14 26 09.21
Dec (J2000): +05 49 30.9

with an uncertainty of 2.7 arcsec (radius, 90% confidence). This
position is 10" from the unenhanced XRT position reported in GCN Circ.
13592. The size of the astrometric correction, which is responsible for
this shift, was such that the enhanced position was initially rejected 
and not circulated automatically. Position enhancement is described by 
Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 
1177).

This corrected position is our best XRT position, and is 1.5 arcsec from
the optical counterpart proposed in GCN Circ. 13591, supporting the
identification of that source as the afterglow. We thank Daniele
Malesani for drawing this to our attention.

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