TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4142
SUBJECT: GRB 051021, SMARTS optical/IR observations
DATE:    05/10/23 01:56:24 GMT
FROM:    Bethany Cobb at Yale U  <cobb@astro.yale.edu>

B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 051021
(GCN 4116, Yoshida et al.) with a mid-exposure time of
2005-10-22 02:53 UT, which is ~13.5 hours post-burst.
Total summed exposure times amounted to 36 minutes in I and 30 
minutes in J.

At the position of the reported afterglow (GCN 4120, Fox et al.), an 
object is marginally detected in our I-band images.  The preliminary 
magnitude of this object is determined to be I = 22.0 +/- 0.4, in 
comparison with several nearby USNO B1.0 stars.

The afterglow candidate is not, however, detected in the J-band.  Using 
several 2MASS comparison stars, the limiting magnitude of this image 
is determined to be J > 19.9 +/- 0.1.  

There is an object near to the position of the afterglow candidate 
(at RA = 1:56:35.6, Dec = 9:04:26.2) that is measured in our image
to have a magnitude of J = 17.2 +/- 0.1.  This object is below the 
detection limits of 2MASS, so it is not detected in the 2MASS 
images (though it is present in the USNO B1.0 survey).  Possibly, this is 
the object reported by Haislip et al. (GRB 4127).  Therefore, in agreement 
with Cenko et al. (GCN 4140), there is not yet clear evidence 
to suggest that this is a high redshift event.