TITLE: GCN CIRCULAR NUMBER: 9168 SUBJECT: GRB 090418: Optical observations with MITSuME Okayama and Ishigaki 1m telescope DATE: 09/04/20 07:23:37 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs D. Kuroda, M. Yoshida, M. Isogai, K. Yanagisawa, Y. Shimizu, S. Nagayama, H. Toda, M. Isogai (NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 090417B (Mangano et al. GCN 9149) with optical three color (g', Rc and Ic) CCD cameras attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory and the 1m telescope of Ishigaki-Jima Observatory. We started the observation at 13:26:42 UT, 8342s after the burst at Okayama. We could not find a new source at the position of the afterglow (Chornock et al. GCN 9148; Mangano et al. GCN 9149; Goad et al. GCN 9154). 3-sigma upper limits to our observations are the following. We used GSC2.3 catalog for flux calibration. Okayama MITSuME observation Mid-UT Td(day) EXP-T g' Rc Ic ------------------------------------------------------------- 13:56:41 0.11736 2940s (49x60s) >19.2 >19.1 >19.0 16:27:25 0.22204 5880s (98x60s) >20.5 >20.3 >20.1 ------------------------------------------------------------- Ishigaki-Jima 1m telescope observation Mid-UT Td(day) EXP-T g' Rc Ic ------------------------------------------------------------- 14:48:36 0.15342 3000s (10x300s) >20.6 >20.9 >19.9 -------------------------------------------------------------