TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3022 SUBJECT: GRB050215B: ROTSE-III optical observations DATE: 05/02/15 04:01:32 GMT FROM: Sarah Yost at U.Michigan S.A. Yost, D.A. Smith, and E.S. Rykoff report on behalf of the ROTSE collaboration: ROTSE3B, located at McDonald Observatory, Texas, responded to GRB050215B (Swift#0106107) under fair conditions (low elevation). An automatic response (interrupting the sequence for 050215A) resulted in a sequence of 60+ images beginning 8 sec after the trigger. The first image was taken at 02:35:19.0, 97 sec after the burst. We took 10 5 sec, 10 20 sec, and 40+ 60 sec exposures. The images are unfiltered and were calibrated relative to USNO A2.0. Individual images have limiting magnitudes from 16-17.7 mag. Comparison to the DSS reveals no new sources within the 3-sigma error circle to a limiting magnitude of 17.8-18.8 for coadded sets of 10 images between 100 sec and 50 min post-burst This message may be cited