TITLE: GCN CIRCULAR NUMBER: 6193 SUBJECT: GRB 070311: MITSuME Okayama Optical Observation DATE: 07/03/11 14:26:37 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, K. Yanagisawa, Y. Shimizu (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We performed optical imaging observation (g', Rc, and Ic) of the field of GRB 070311 (Mereghetti et al. GCN 6189) with 50cm MITSuME telescope at Okayama Astrophysical Observatory from UT 10:11 to UT 12:03 on Mar.11 2007. We coadded 76 CCD frames for each band. Exposure time of each frame is 1 minute. We made flux calibration using USNO B1.0 catalg. No new source was found around the position of the IR source reported by Covino et al. (GCN 6190) and the XRT source reported by Guidorzi (GCN 6192). Three sigma limiting magnitudes of our observation are listed below. ---------------------------------------------------- band mid-UT exp.time upper limit g' Mar. 11 11:07 76 x 1 min. 20.7 mag Rc Mar. 11 11:07 76 x 1 min. 21.0 mag Ic Mar. 11 11:07 76 x 1 min. 19.2 mag ----------------------------------------------------