[vsnet-grb-info 20879] GRB 180720B: Kanata 1.5m optical/NIR observation

[GCN Circulars]

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  <kawabtkj at hiroshima-u.ac.jp>

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.