TITLE: GCN CIRCULAR NUMBER: 18440 SUBJECT: GRB 151022A: MITSuME Okayama Ks-band upper-limit DATE: 15/10/22 15:51:57 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 151022A (D'Avanzo et al., GCN 18436) in Ks-band with a wide-field near infrared imager at Okayama Astrophysical Observatory (Japan). The imager has effective aperture of 0.91 m. Observations started from 14:13 UT on 22th October, 0.12h after the BAT trigger, to 14:56 UT. The total exposure of 17.0 min was successfully obtained. In our co-add image, we did not find any new point source within the enhanced XRT error circle (Evans et al., GCN 18438) down to limiting magnitude of Ks=14.8 (Vega, S/N=10). The photometric calibration was made against 2MASS field stars. T0+[sec] MID-UT T-EXP[sec] Ks --------------------------------------------------- +1,721 14:35 1,020.0 >14.8 --------------------------------------------------- T0+ : Elapsed time after the burt [sec] T-EXP: Total Exposure time [sec]