TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4387 SUBJECT: GRB 051221B: ROTSE-III Optical Limits DATE: 05/12/22 14:52:55 GMT FROM: Brad Schaefer at LSU B. E. Schaefer (Louisiana State Univ.) report on behalf of the ROTSE collaboration: ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe, Turkey, responded to GRB 051221B (Swift trigger 173904), producing images beginning 10 s after the GCN notice time. An automated response took the first image at 20:06:57.2 UT, 217.1 s after the burst, under excellent conditions. We took 10 5-sec, 138 20-sec eposures. These unfiltered images are calibrated relative to USNO A2.0 (R). Comparison to the DSS (second epoch) reveals no new sources within the 3-sigma error circle, for both single images and coadding into sets of 10. In particular, we find nothing unusual inside the Swift XRT positional circle (Fenimore et al. GCN4382). Individual images have limiting magnitudes ranging from 15.1-17.1; we set the following specific limits. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 20:06:57.2 20:07:02.2 5 16.6 217.1 N 20:06:57.2 20:09:02.9 125 17.4 217.1 Y