TITLE: GCN CIRCULAR NUMBER: 18171 SUBJECT: GRB 150818A: MITSuME Akeno optical upper limits DATE: 15/08/19 12:38:55 GMT FROM: Taketoshi Yoshii at Tokyo Tech T.Fujiwara, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, Y. Yano, S. Kurita, Y.Ono, S.Harita,Y.Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 150818A (V. D'Elia et al. GCN Circular #18152) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2015-08-18 11:54:53 UT (~18 min after the burst). We did not find any new point source within XRT circle in all three bands. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic --------------------------------------------------------------------------------------- 1101 11:59:46 540 >19.4 >19.4 > 18.5 --------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration