[vsnet-grb-info 2531] GRB 051221: Improved astrometry of the IR counterpart

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4368
SUBJECT: GRB 051221: Improved astrometry of the IR counterpart
DATE:    05/12/21 07:20:22 GMT
FROM:    Josh Bloom at UC Berkeley  <jbloom at astron.berkeley.edu>

J. S. Bloom (UC Berkeley) reports:

We have reduced the second epoch of our PAIRITEL imaging (beginning  
2005-12-21 03:02:32 UTC; total integration = 690 sec) and detect the  
source mentioned in GCN 4367 in a stacked mosaic. The source appears  
to be best detected in the full stack J-band image at a revised  
position of J2000:

     21:54:48.662 +16:53:26.97

The uncertainty relative to the USNOB1.0 is 180 mas in each  
coordinate (the previous two circulars were based upon an astrometric  
match using far fewer 2MASS sources in the field). This position is  
1.41 arcsec from the Burrows et al. XRT position (GCN 4366). Because  
the source is observed near the detection level, we cannot confirm  
fading behavior at this time. Still, given the proximity to the XRT  
location, we advance that this source is the IR counterpart to GRB  
051221 (GCN 4363). If so, this would be the first infrared  
counterpart detected for a short-hard GRB.

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