TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4386 SUBJECT: GRB 051221B: TAROT optical limits DATE: 05/12/22 12:11:37 GMT FROM: Alain Klotz at CESR-CNRS Klotz, A. (CESR-OMP), Boer M. (OHP), and Atteia, J.L. (LAT-OMP) report: We imaged the entire field of GRB 051221B (173904) detected by SWIFT (Boyd et al. GCNC 4376) with the TAROT robotic telescope (D=25cm) located at the Calern observatory, France. Observations started 9 seconds after the GCN notice (and 216 sec. after the GRB). The field had an elevation of 35 degrees above horizon at the beginning of the observations and then decreased. The humidity was rather high (90%), and haze appeared after few minutes of observation. We compared the ± 1.6 arcmin field centred on the XRT position (Fenimore et al. GCNC 4382) with stars of the USNO-B1 catalogue and with the DSS2-R atlas. We did not find any new source. Following is the observation log and the upper limits we derived: Since-trig Mag. start end +216s to +276s R>14 +282s to +312s R>18.2 +319s to +349s R>18.2 This message may be cited.