GCN Circular 14633

D. A. Perley (Caltech) reports on behalf of a larger collaboration:

The Palomar 60-inch telescope automatically responded to GRB 130427A 
(Sonbas et al., GCN 14632
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 ) and slewed to the position as soon as the 
source became observable a few minutes after the GRB alert.  A series of 
r, i, and z-band exposures was taken at very high airmass (~4) starting 
at 07:25:33 UT, 11.85 minutes after the BAT trigger.

The field is crowded, and contains a small globular cluster (GCl 114) 
centered at RA=19:45:14.40 Dec=-08:00:26.0 (J2000), 2.5 arcminutes from 
the GRB.

We do not detect any source at a position coincident with the XRT 
position in individual images.  A stack of the first five r-band images 
(spanning from 12-27 minutes after the GRB) shows no clear object at 
this position to a limiting magnitude of R > 19.6 mag (3 sigma), 
although there is a marginal detection of a source inside the error 
circle slightly below this level, centered at RA=19:45:07.27, 
Dec=-07:58:42.3 (J2000, +/-1.5 arcsec).  It is also apparent in similar 
r- and z-band stacks, and so is probably real.  The source may also be 
marginally present in the DSS imaging, although it is not in the USNO 
B1.0 catalog.

The association of the GRB with the globular cluster (or the optical 
source) is unclear; this could be an unusual Galactic event or a chance 
alignment of an ordinary extragalactic GRB (with a faint optical 
afterglow) with these objects. Further observations are encouraged.