TITLE: GCN CIRCULAR NUMBER: 29820 SUBJECT: IceCubeCascade-210416a: Kanata Optical Imaging of 3C 279 DATE: 21/04/16 03:40:53 GMT FROM: Mahito Sasada at Hiroshima University Mahito Sasada, Ryo Imazawa, Tatsuya Nakaoka (Hiroshima U.); Masayuki Yamanaka (Kyoto U.); Shigeo Kimura (Tohoku U.); Yousuke Utsumi (Stanford/SLAC) A GCN/AMON notice from IceCube collaboration ( https://gcn.gsfc.nasa.gov/gcn/notices_amon_icecube_cascade/135196_31863828.amon) reported an IceCube Cascade Event 210416a. We noticed that 3C 279 which was a known QSO at a redshift of 0.54 resided in the center of the error region. Kanata/HONIR has also observed 3C 279 for the past few days and identified that 3C 279 exhibited a brightness decrease of ~0.5 mag in the R band from MJD=59315.651869 (2021/04/11) to MJD=59318.620938 (2021/04/14). We will continue the monitoring observation of 3C 279. Kanata/HONIR is an optical and near-infrared simultaneous imager, spectrograph, and polarimeter equipped on the 150 cm Kanata telescope at Higashi-Hiroshima Observatory in Japan (Akitaya et al. 2014, Proc. SPIE 9147, 91474O).