TITLE: GCN CIRCULAR NUMBER: 21249 SUBJECT: LIGO/Virgo G288732: Kiso/KWFC optical imaging of the possible Fermi/LAT counterpart DATE: 17/06/12 11:26:22 GMT FROM: Tomoki Morokuma at U.TokyoJ-GEM Tomoki Morokuma (The University of Tokyo), Masaomi Tanaka (National Astronomical Observatory of Japan), Nozomu Tominaga (Konan University), Shigeyuki Sako, Ryou Ohsawa, Mamoru Doi, Kentaro Motohara (The University of Tokyo) on behalf of J-GEM collaboration We report optical imaging follow-up observations in an error region of the possible electromagnetic counterpart of G288732 (GCN 21221) discovered with Fermi LAT (Omodei et al. 2017, GCN, 21227). We observed the field with 1.05-m Kiso Schmidt telescope and its 2.2 deg x 2.2 deg field-of-view camera, Kiso Wide Field Camera (KWFC; Sako et al. 2012, SPIE, 8446, 84466L). We took two consecutive 1-sec exposures twice in i-band on June 9.483, 9.489, 9.527, and 9.529, 2017 UT, roughly 123 ks after the GW detection. The median depth of the images is 15.6 mag (AB, 5 sigmas). Although there is a 1.5 arcmin gap in Declination because of the spatial gap of the CCDs, we covered almost the entire error field of the possible Fermi LAT detection. We compared the detected source catalogs with the public Pan-STARRS1 catalog (Chambers et al. 2016, arXiv:1612.05560) and do not find any new transient sources within the Fermi LAT error circle. All the seven Swift XRT sources reported in Evans et al. (2017, GCN 21233) were covered by our observations and the source 7 is detected in our images with almost constant brightness of i=12.8 mag. [GCN OPS Note(14jun17): Per author's request, the phase "were covered by our observations" was added to the last sentence.]