TITLE: GCN CIRCULAR NUMBER: 23968 SUBJECT: GRB190311A: MITSuME Akeno optical observation DATE: 19/03/15 12:11:13 GMT FROM: Kota Iida at Tokyo Inst. of Tech. K. Iida, R. Itoh, K. L. Murata, Y. Tachibana, S. Harita, K. Morita, K. Shiraishi, M. Oeda, M. Niwano, R. Adachi, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration We searched for the optical counterpart of GRB 190311A (Troja et al., GCN Circular #23946) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 14:24:43.64 UT which corresponds to 70 sec after the trigger. We detected the point source at the position consistent with the afterglow detected previously (Troja et al. GCN #23946; Pozanenko et al. GCN #23947; Zhu et al. GCN #23948; Gorbovskoy et al. GCN #23949, Belkin et al. GCN #23951). The measured magnitudes are listed as follows. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~70 14:24:46.22 540 18.9+/-0.2 18.6+/-0.2 18.2+/-0.2 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration. The magnitudes are expressed in the Vega system.