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GCN Circular 514

GRB 991216 VLBA Observations
2000-01-03T18:39:40Z (24 years ago)
Greg Taylor at NRAO <>
G. B. Taylor and D. A. Frail (NRAO) report on behalf of a larger

"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."

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