TITLE: GCN CIRCULAR NUMBER: 6123 SUBJECT: GRB 070220: MITSuME Okayama Optical Observation DATE: 07/02/21 09:43:09 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, K. Yanagisawa, (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We performed optical imaging observation of the field of GRB 070220 (GCN 6114, GCN 6118) with 50cm MITSuME telescope at Okayama Astrophysical Observatory from UT 9:57 to UT 12:11 on Feb. 20 2007. We coadded 105 Ic band frames with a 1 minute exposure time. We made flux calibration using USNO B1.0 catalg. The three sigma limiting magnitude of our observation was 20.2 in Ic band. We could not find optical afterglow candidate in the error circle reported in GCN 6118. ---------------------------------------------------- band mid-UT exp.time upper limit Ic Feb. 20 11:24 105 x 1 min. 20.2 mag ----------------------------------------------------