TITLE: GCN GRB OBSERVATION REPORT NUMBER: 212 SUBJECT: GRB 990123 radio observations DATE: 99/01/24 19:19:16 GMT FROM: Titus Galama at U.Amsterdam T.J. Galama, P. Vreeswijk, E. Rol (U. of Amsterdam), R. Strom (NFRA and U. of Amsterdam), J. van Paradijs (U. of Amsterdam and U. of Alabama in Huntsville), C. Kouveliotou (USRA/MSFC), G. de Bruyn (NFRA and U. of Groningen) report: "We observed the error box of GRB 990123 (GCN #199) at 4.88 GHz with the Westerbork Synthesis Radio Telescope (WSRT) for 12 hours on January 24.28 1999 UT. At the position of the optical transient (GCN #201) we do not detect a radio source (< 130 microJansky; 3 sigma). This result, when compared with the January 24.65 UT 8.46 GHz VLA detection (260 +/- 32 microJansky; GCN #211) may be due to synchrotron self-absorption, or otherwise, may indicate that the 4.88 GHz observation was suppressed by interstellar scintillation. Further observations are planned." This message is citeable.