TITLE: GCN CIRCULAR NUMBER: 22670 SUBJECT: GRB 180418A: MITSuME Ishigakijima Optical Observation DATE: 18/04/24 02:00:28 GMT FROM: Ryosuke Itoh at Tokyo Institute of Tech. T. Horiuchi, H. Hanayama, M. Honma (IAO, NAOJ), R. Itoh, K. Shiraishi, K. Murata, Y. Tachibana and N. Kawai (Tokyo Tech) report on behalf of the MITSuME and OISTER collaboration: We observed the field of GRB 180418A (D'Elia et al.,GCN 22646) with the optical three color (g', Rc and Ic) CCD camera attached to the Murikabushi 1m telescope of Ishigakijima Astronomical Observatory. The observation started on 2018-04-18 13:55:32 UT, (~7 hours after the burst). We detected the previously reported afterglow (W. Zheng and A. Filippenko, GCNC22647) in the R band. The photometric results of the OT are listed below. We used UCAC-4 catalog for flux calibration. #T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------- 8.6 15:22:01 10380 >22.8 22.4+/-0.5 >22.0 ------------------------------------------------------------------- T0+ : Elapsed time after the burst [hour] T-EXP: Total Exposure time [sec]