TITLE: GCN GRB OBSERVATION REPORT NUMBER: 514 SUBJECT: GRB 991216 VLBA Observations DATE: 00/01/03 18:39:40 GMT FROM: Greg Taylor at NRAO G. B. Taylor and D. A. Frail (NRAO) report on behalf of a larger collaboration: "Following the detection of the radio afterglow on Dec 18.16 (Taylor & Berger, GCN 483) from the bright BATSE burst GRB 991216 (Kippen et al., GCN 463) we observed with the Very Long Baseline Array (VLBA) for 2 hours beginning on December 18.32 UT. The flux density measured at 8.4 GHz was 705 +/- 85 microJy. The source is unresolved by these observations with a size less than 1 mas (size < 6.6 pc given the probable redshift of 1.02 reported by Vreeswijk et al. in GCN 496). The VLBA position is at ra = 05h09m31.2983s dec = +11d17'07.262" (equinox J2000) with a conservative error of 0.001 arcsec in each coordinate. This position is within 0.02 arcsec of the radio position derived by Taylor & Berger (GCN 483) who claim an uncertainty of 0.1 arcsec, but is 0.321 arcsec from the optical afterglow position reported by Dolan et al. (GCN 486) who claim an uncertainty of 0.15 arcsec. Given that the optical and radio afterglow should be coincident, we suggest that the optical astrometric position given by Dolan et al. suffers from a systematic error." This message may be cited.