TITLE: GCN CIRCULAR NUMBER: 25906 SUBJECT: GRB 191001B: MITSuME Akeno optical upper limits DATE: 19/10/01 18:52:08 GMT FROM: Katsuhiro L. Murata at Nagoya U K. L. Murata, R. Adachi, M. Oeda, K.Shiraishi, K. Iida, M. Niwano, F. Ogawa, R. Hosokawa, S. Toma, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 191001B (E. Troja et al., GCN Circular #25902) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 17:22:09 UT. We did not find any new point sources within the BAT on-board calculated error circle in all three bands. We obtained the following 5-sigma limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ ~169 ~17:37 1680 g'>18.8, Rc>18.8, Ic>18.6 ------------------------------------------------------------------------------------------------ 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 AB system.