TITLE: GCN CIRCULAR NUMBER: 22754 SUBJECT: GRB 180602A: MITSuME Okayama optical upper limits DATE: 18/06/02 12:30:27 GMT FROM: Yutaro Tachibana at Tokyo Tech Y. Tachibana, R. Itoh, K. L. Murata, S. Harita, K. Morita, T. Ozawa, H. Mamita, K. Shiraishi, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 180602A (Cenko et al., GCN Circular #22752) 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 2018-06-02 11:14:03.47 UT (~3 hours after the burst). We did not find any new point source within the enhanced XRT error circle (Osborne et al., GCN Circular #22753) in all the three bands. We obtained following limits for the magnitudes. T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~3.07 ~11:18:47 420 >17.8 >17.7 >17.1 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.