TITLE: GCN CIRCULAR NUMBER: 20892 SUBJECT: GRB 170317A: MITSuME Okayama Ks-band upper-limit DATE: 17/03/17 16:39:39 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 170317A (LaPorte et al., GCN 20885) 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 09:54 UT on 17th March, 8 min after the BAT trigger, to 10:38 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 XRT error circle (Beardmore et al., GCN 20887) down to the limiting magnitude of Ks=16.1 (Vega, S/N=5). The photometric calibration was made against 2MASS field stars. T0+[sec] MID-UT T-EXP[sec] Ks --------------------------------------------------- +1,819 10:16 1020.0 >16.1 --------------------------------------------------- T0+ : Elapsed time after the burt [sec] T-EXP: Total Exposure time [sec]