TITLE: GCN CIRCULAR NUMBER: 26019 SUBJECT: GRB191016A: MITSuME Okayama optical observation DATE: 19/10/17 11:15:15 GMT FROM: Sayaka Toma at Tokyo Institute of Technology S. Toma, M. Niwano, R. Adachi, K. L. Murata, M. Oeda, K.Shiraishi, K. Iida, F. Ogawa, R. Hosokawa, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 191016A (J.D. Gropp et al., GCN Circular #26008) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Okayama Astrophysical Observatory, Okayama, Japan. The observation started on 09:37:49.50 UT which corresponds to 5.5 hours after the trigger. We detected the point source at the position consistent with the afterglow detected previously (Alan M. Watson et al. GCN #26010). The measured magnitudes and 3-sigma limit are listed as follows. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ——————————————————————————————————————————————————— 20794 13:31:46 20040 19.5+/-0.4 > 19.0 18.6+/-0.2 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 and UCAC4 catalog for flux calibration. The magnitudes are expressed in the Vega system.