TITLE: GCN CIRCULAR NUMBER: 20223 SUBJECT: GRB 161129A: MITSuME Okayama Ks-band Observation DATE: 16/12/01 05:38:35 GMT FROM: Kenshi Yanagisawa at OAO/NAOJ K. Yanagisawa, D. Kuroda, Y. Shimizu, H. Izumiura (OAO/NAOJ), M. Yoshida (Hiroshima), K. Ohta(Kyoto), and N. Kawai(Tokyo Tech.) report on behalf of the MITSuME collaboration: We observed the field of GRB 161129A (Kocevski et al., GCNC 20210) in Ks-band with a wide-field NIR camera at Okayama Astrophysical Observatory (Japan). The camera has an effective aperture of 0.91m. Observations started from 08:44 UT on 29th November, 93 min after the BAT trigger, to 09:29 UT. The total exposure of 17.3 min was successfully obtained. In our co-add image, we found a faint source at coordinates R.A.(J2000) = 21:04:54.59 DEC (J2000) = +32:08:05.2, close to the position reported by Beardmore et al.(GCNC 20211), and Klose & Stecklum (GCNC 20216). We measured the source magnitude of Ks = 15.95 +/- 0.14 (Vega). The calibration was made against 2MASS field stars. T0+[min] MID-UT T-EXP[min] Ks ------------------------------------------------------------ +115 09:06 17.3 15.95 +/- 0.14 (Vega) ------------------------------------------------------------ T0+ : Elapsed time after the burst [min] T-EXP: Total Exposure time [min]