TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4392 SUBJECT: GRB 051221A: MDM Optical Observations DATE: 05/12/23 23:04:14 GMT FROM: Markus Boettcher at Ohio U M. Boettcher and M. Joshi (Ohio University) report: Starting on 21 Dec., UT 04:02, we observed the optical afterglow of GRB 051221A (Parsons et al. GCN 4363) with the MDM 1.3 m telescope in three 600 s exposures (beginning 2.1, 2.4, and 2.6 hr after the trigger). We detect a faint source consistent with the locations of the IR (Bloom, GCN 4367 and 4368), optical (Berger, GCN 4369, 4371; Berger and Soderberg, GCN 4375; Berger et al. GCN 4383), and X-ray (Burrows et al., GCN 4366; Grupe et al. GCN 4389) afterglows. Photometry, calibrated on the R-band magnitudes of 6 comparison stars in our field of view as given by Aladin, from the UCD data base (UCD: PHOT_PHG_R), yields the following magnitude estimates (t = time after GRB trigger): t | R ------------------- 2.1 hr | 19.88 +/- 0.40 2.4 hr | 19.93 +/- 0.39 2.6 hr | 19.98 +/- 0.34 Consequently, there is no evidence for variability between the three frames. Seeing was rather poor (~ 2 arc sec.), so the optical afterglow is not resolved from the host galaxy (Soderberg and Berger, GCN 4375). Given the RAPTOR upper limit on the fading counterpart of R > 20.2 at 1.3 hr after the trigger (Wren et al., GCN 4380), our measurement might in fact be dominated by the host galaxy contribution. This message may be cited.