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GCN Circular 2129

GRB 030329 VLBA Observations
2003-04-10T03:32:38Z (21 years ago)
Greg Taylor at NRAO <>
G. B. Taylor (NRAO), E. Berger (Caltech), D. A. Frail (NRAO), and
S. R. Kulkarni (Caltech) report:

"Following the detection of the radio afterglow on Mar 30 (Berger
et al. GCN 2014) from the bright burst GRB 030329 (GCN 1985, 1997)
we observed with the Very Long Baseline Array (VLBA) for
8 hours beginning on April 01.05 UT.  The flux density measured at
8.4 GHz was 8.3 +/- 0.4 mJy.  The source is unresolved by these
observations with a size less than 0.5 mas (size < 1.4 pc given the
redshift of 0.1685 reported by Greiner et al. in GCN 2020).
Assuming typical parameters for the expansion (e.g. Frail et al. 2000, 
ApJ, 534, 559) we expect a size of about 1.3e17 cm
(0.04 pc) at the time of the VLBA observation (t=2.7 days).
The VLBA position is at ra = 10h44m49.9595s dec = +21d31'17.438"
(equinox J2000) with a conservative error of 0.001 arcsec in each
coordinate.  This position is within 0.02 arcsec of the VLA radio position,
but is 1.21 arcsec from the optical afterglow position
reported by Yamaoka et al. (GCN 1994) who claim an uncertainty of 0.07
arcsec.  Given that the optical and radio afterglow should be
coincident, we suggest that the optical astrometric position 
suffers from a systematic error.

High frequency VLBI observations are planned with the goal of 
eventually resolving the radio afterglow."

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