TITLE: GCN CIRCULAR NUMBER: 10678 SUBJECT: GRB100423A: MITSuME optical upper limits DATE: 10/04/25 08:13:10 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 100423A (Stroh et al. GCNC 10651) 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 2010-04-23 13:27:35 UT (~12.9h after the burst). We could not detect the previously reported afterglow (Filgas et al., GCN 10652) in all the three bands. Three sigma upper limits of the OT are listed below. We used SDSS catalog for flux calibration. T0+[day] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------ 0.59033 14:45:04 4500.0 >18.9 >19.0 >18.4 ------------------------------------------------------ T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]