TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3392
SUBJECT: GRB 050509b: Precision Astrometry
DATE:    05/05/09 11:12:47 GMT
FROM:    Josh Bloom at Harvard/CFA  <jbloom@cfa.harvard.edu>

J. Bloom (UCB), C. Blake (Harvard), J. X. Prochaska (UCSC), J. Hennawi
(UCB), M. Gladders (Carnegie), B. Koester (U Michigan) and H. W. Chen
(MIT) report:

Connecting a WIYN 600s Sloan r band image to compact astrometric sources
in the 2MASS catalogue we find the following refined position for the
putative host (Bloom et al. GCN #3386) at redshift z=0.226 (Prochaska et
al. GCN #3390) and counterpart (Bloom et al. GCN #3388):

        galaxy:  RA = 12:36:12.87, Dec = 28:58:58.5
   counterpart:  RA = 12:36:13.67, Dec = 28:58:57.0

(J2000; absolute uncertainty of 200 milliarcsec in each direction). The
proposed counterpart is thus 1.51" S, 10.41" E from the galaxy and 1.61"
S, 0.88" E of the XRT position (Kenea et al. #3383). This distance of 1.84
arcsec is well within the astrometric uncertainty of the XRT position. The
position reported here is consistent with that reported in Cenko et al.
GCN #3391.

Another zoom in image is now posted at:
  http://astro.berkeley.edu/~jbloom/grb050509b-zoom.ps
  http://astro.berkeley.edu/~jbloom/grb050509b-zoom.gif

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