TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4396 SUBJECT: GRB051117B: optical observation DATE: 05/12/27 16:02:46 GMT FROM: Daisaku Nogami at Kyoto U D. Nogami, T. Kawamura, J. Kuriyama, K. Sugiyasu, K. Kubota (Kyoto Univ.), K. Yanagisawa (Okayama Astrophys. Obs.), S. Kouzuma, H. Yamaoka (Kyushu Univ.), and N. Kawai (Tokyo Inst. of Tech.) report: We observed the field of GRB051117B (Band et al., GCN 4281) with a 50-cm telescope (MITSuME) at the Okayama Astrophysical Observatory, using a three-color (g', Rc, and Ic) CCD imager. The observations started at 14:16:22 (UT), about 54 min after the trigger time, and ended at 16:36:46 (UT). The exposure time was 60 sec, and we obtained 110 images in each band. We could not find any afterglow candidate around the error box of GRB051117B (GCN 4281). The 3-sigma upper limits in the stacked images of each band are 19.2 mag, 19.2 mag, and 19.5 mag in the g', Rc, and Ic band, respectively. These magnitudes were calibrated with the catalogs of Tycho (VT), USNO A2.0 (R), and USNO B1.0 for g', Rc, and Ic, respectively.