TITLE: GCN CIRCULAR NUMBER: 10641 SUBJECT: GRB 100414A: CFHT optical observations DATE: 10/04/21 10:17:20 GMT FROM: Yuji Urata at Nat. Central U. Y. Urata (NCU) and K.Y Huang (ASIAA) on behalf of EAFON report; "We observed the location of the GRB100414A optical afterglow (Cucchiara et al. 10608) with CFHT on the night of April 19 (5.2 day after the trigger) and 20 (6.2 day). The g', r' and i' band images show the afterglow clearly. We estimate preliminary magnitudes of r'=22.46+/-0.05 (5.19 day) and r'=22.84+/-0.05 (6.17 day) against the SDSS field stars. Combined with the photometric results reported by Filgas et al (10607) and Cucchiara (10606), the optical afterglow light curves are well described by a simple power law decay with the temporal index about 2.5."