TITLE: GCN CIRCULAR NUMBER: 11258 SUBJECT: GRB100901A: IAO optical upper limits at 4 days after the burst DATE: 10/09/08 18:36:26 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda (OAO, NAOJ), H. Hanayama, T. Miyaji, J. Watanabe (IAO, NAOJ), K. Yanagisawa (OAO, 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 100901A (Immler et al., GCN 11159) 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 2010-09-05 19:53:16 UT (~4.3 day after the burst). We did not detect the previously reported afterglow (Immler et al., GCN 11159 and many follow-up observations) 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 ------------------------------------------------------ 4.26159 19:50:52 1080.0 >21.6 >21.3 >19.8 ------------------------------------------------------ T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]