TITLE: GCN GRB OBSERVATION REPORT NUMBER: 210 SUBJECT: GRB990123 optical observations DATE: 99/01/24 15:35:49 GMT FROM: Paul Vreeswijk at U of Amsterdam Eran Ofek and Elia M. Leibowitz, Wise Observatory, Tel Aviv University report: >From 4 CCD frames of the object taken at the WO between Jan 24.0617-24.1162 we have determined an average R magnitude of 19.87+-0.2, with calibration based on 4 USNO A2.0 stars. The decay parameter in the R band over that time interval is -1.9+-0.1. On Jan 24.0625, the color index of the object was B-R=-0.48+-0.25. This report may be cited.