TITLE: GCN CIRCULAR NUMBER: 18968 SUBJECT: GRB 160131A: MITSuME Ishigakijima Optical Observation DATE: 16/02/01 02:05:16 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda (OAO, NAOJ), H. Hanayama, T. Miyaji, J. Watanabe (IAO, NAOJ), K. Yanagisawa (OAO, NAOJ), S.Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of the MITSuME and OISTER collaboration: We observed the field of GRB 160131A (Pagani and Barthelmy, GCNC 18951) with the optical three color (g', Rc and Ic) CCD camera attached to the Murikabushi 1m telescope of Ishigakijima Astronomical Observatory. The observation started on 2016-01-31 14:06:17 UT (~5.8 h afterthe burst). We detected the previously reported afterglow (Pagani and Barthelmy, GCNC 18951; Yurkov et al., GCNC 18952; Guidorzi et al., GCNC 18953) in all the three bands. Photometric results of the OT are listed below. We used GSC2.3 catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' g'_err Rc Rc_err Ic Ic_err ----------------------------------------------------------------------- 0.24373 14:11:29 540.0 17.92 0.09 17.19 0.05 16.88 0.06 ----------------------------------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]