TITLE: GCN CIRCULAR NUMBER: 22838 SUBJECT: GRB 180624A: MITSuME Okayama optical upper limits DATE: 18/06/25 04:46:32 GMT FROM: Ryosuke Itoh at Tokyo Institute of Tech. R. Itoh, K. L. Murata, Y. Tachibana, K. Morita, K. Shiraishi, M. Oeda, R. Adachi, K. Iida, S. Niwano, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 180624A (S. L. Gibson et al., GCN Circular #22832) 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 2018-06-24 13:51:38.54 UT (~118 sec after the burst). We did not find any new point source within the enhanced XRT error circle in all the three bands. We obtained following limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~118 ~13:52:08 60 >15.5 >16.1 >16.2 ~1537 ~14:15:47 2100 >17.2 >17.7 >17.6 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used UCAC-4 catalog for flux calibration.