GCN Circular 3416

J. S. Bloom, R. J. Foley, D. Pooley, A. V. Filippenko, R. Chornock (UCB),
C. Blake (Harvard), J. X. Prochaska (UCSC), J. Hennawi (UCB), M. Gladders
(Carnegie), B. Koester (U Michigan) and H. W. Chen (MIT) report:

We observed the field of GRB 050509b (#3383,#3385) with Keck I (+LRIS)
with g' and R filters.  Starting at 20050511.25 UT, we took 5 dithered
images in each band for a total of 1660 and 1620 sec exposures in g and R,
respectively. At the location of the two reported Chandra sources we find
no significantly-detected flux in either band, however there are
indications of an R counterpart (at the few sigma level) to Chandra#8.
Moreover, these images do reveal a number of sources in the XRT fainter
than reported deep imaging with the VLT (3410) and Keck II (3401), which
we label J1-J4:

   J1 12:36:13.56 +28:59:03.4
   J2       13.44        04.7
   J3       13.41     58:56.3
   J4       13.47     59:06.2

(J2000; estimated errors of 0.3 arcsec in each direction).

We note that S5, which is less than 2 arcsec from the Chandra source #5,
appears bluer than neighboring S3 and S2.

The finding chart can be found at:
 http://astro.berkeley.edu/~jbloom/grb050509b-chandra-keck-combo.gif