[vsnet-grb-info 4146] GRB 061217: Astrometry-Corrected XRT Position

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  5953
SUBJECT: GRB 061217: Astrometry-Corrected XRT Position
DATE:    06/12/21 22:50:35 GMT
FROM:    Nat Butler at MIT/CSR  <nrbutler at space.mit.edu>

N. Butler (U.C. Berkeley) reports:

We centroid on a faint and fading source 20" away from the initial refined
XRT team position (GCN5932).  Using 6 optical/X-ray matches, we find an
astrometry corrected position (v2.9) relative to 2MASS of:

  RA, Dec:  10 41 39.32  -21 07 22.1 ;  +/-3.8" (90% Conf.)     (J2000.0)

The candidate from GCN5948 is 14" from our position, however this is likely
a star (GCN5949).  Our position is 5.7" away from Source G1 in GCN5949 and
11.4" away from Source G2 in GCN5949.  Our position therefore favors
associating source G1 with the short GRB host galaxy.

Our position has remained stable for several days as new XRT data
reach our computers (http://astro.berkeley.edu/~nat/swift/xrt_pos.html).
The reductions, which take into account bad detector columns, are described in
Butler (2006; AJ accepted; astro-ph/0611031).  The disagreement of our
position with the original XRT team refined position lead to a retraction
of that position.  The new XRT team position (GCN5947) is consistent with
ours.

Thanks to J. Bloom and A. Kann for helping to discover the discrepancy
with the XRT Team position.