TITLE: GCN CIRCULAR NUMBER: 11205 SUBJECT: GRB10901A: Optical observations at IAO DATE: 10/09/04 13:33:16 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. Our observations started on 2010-09-02 13:22:45 UT (~1.0 day after the burst) and 2010-09-03 15:24:41 UT (~2.1 day after the burs). We detected the previously reported afterglow (Immler et al., GCN 11159; Guidorzi et al., GCN 11160; Kuroda et al., GCN 11172; Kuroda et al., GCN 11189; Ukawatta et al., GCN 11198) in all the three bands. Photometric results of the OT are listed below. We used SDSS catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' g'_err Rc Rc_err Ic Ic_err ---------------------------------------------------------------------- 1.04604 14:40:28 1560.0 19.49 0.04 18.86 0.04 18.25 0.05 1.08548 15:37:16 1560.0 19.59 0.04 18.93 0.04 18.41 0.06 1.14442 17:02:08 1500.0 19.64 0.05 19.11 0.04 18.50 0.07 2.13035 16:41:52 4020.0 20.71 0.08 19.96 0.06 20.04 0.17 ---------------------------------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]