TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4364 SUBJECT: GRB 051221: IR Observations at GRB+1hr DATE: 05/12/21 04:45:45 GMT FROM: Josh Bloom at UC Berkeley J. S. Bloom (UC Berkeley), on behalf of a larger collaboration, reports: "We began observations of the bright short burst GRB 051221 (Parsons GCN #4363) with the PAIRITEL 1.3m at 2005-12-21 02:54:02 UTC, about 30 minute after the GCN circular and 1hr3min after the GRB. In a stack of the first 313sec, we detect no new sources to at least the 2MASS limit in JHKs bands. A visual comparison with the DSS-2 (F- plate) shows that most of the sources fainter than 2MASS in the PAIRITEL mosaics have optical counterparts. Some of the faintest IR sources do not have detected counterparts but this is likely due to the redness/faintness of the sources. In particular, we point out objects at J2000: A: 21:54:57.84 +16:53:07.5 (inside the error circle) B: 21:55:00.89 +16:56:50.2 (red, outside the error circle) C: 21:55:01.58 +16:57:07.1 (red, outside the error circle, extended) Further analysis is ongoing but we suggest that these sources be monitored for variability, especially object A." A RGB (=KsHJ) finding chart may be found at: http://astro.berkeley.edu/~jbloom/grb051221.ps This message may be cited.