TITLE: GCN CIRCULAR NUMBER: 22977 SUBJECT: GRB 180720B: Kanata 1.5m optical/NIR observation DATE: 18/07/20 16:21:08 GMT FROM: Koji Kawabata at HASC,Hiroshima U M. Sasada, T. Nakaoka, M. Kawabata, N. Uchida, Y. Yamazaki, K. S. Kawabata (Hiroshima Univ.) report on behalf of Kanata team: We performed optical and NIR imaging polarimetry to the field of the GRB 180720B (Siegel et al. GCN 22973; Martone et al. GCN 22976) from 2018-07-20 14:22:57 UT (73 seconds after the trigger) with HOWPol and HONIR attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Japan. We detected a bright optical counterpart of the GRB within the the Swift-XRT error circle of the X-ray afterglow. The magnitude of the optical counterpart was R~9.4 mag in our first frame taken with 30 second exposure and then smoothly declined. Further analysis is ongoing.