TITLE: GCN CIRCULAR NUMBER: 13817 SUBJECT: GRB 120923A: MITSuME Okayama Optical upper limits DATE: 12/09/25 05:54:47 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 120923A (Yershov et al., GCNC 13796) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory. The observation started on 2012-09-23 10:00:39 UT (~4.7 h after the burst) We did not find any new point source within the enhanced XRT circle (Goad et al., GCNC 13801) in all the three bands. We also could not detect the previously reported afterglow (Levan et al., GCNC 13802). Three sigma upper limits of the OT are listed below. We used SDSS catalog for flux calibration. T0+[day] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------ 0.23958 11:01:05 6360.0 >20.6 >20.2 >18.9 ------------------------------------------------------ T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]