GCN Circular 18400
K. S. Kawabata, R. Itoh, M. Kawabata, T. Nakaoka, H. Mori, K. Takaki (Hiroshima Univ.), and R. Shimotani (Kagawa Univ.) report on behalf of Kanata team: We performed a series of optical imaging-polarimetry for the optical afterglow of GRB151006A (Kocevski et al., GCN 18398) from 73 sec after the Swift/BAT trigger with HOWPol attached to the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Japan. We could not detect any afterglow within the XRT error circle reported in the GCN 18398. We obtained the following preliminary upper limits in our first image (mid-time 88 sec after the trigger) calibrated with UCAC4: Rc > 17.7 Further analysis is ongoing.