TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  350
SUBJECT: GRB 990506 Radio Transient
DATE:    99/06/15 18:28:45 GMT
FROM:    Greg Taylor at NRAO  <gtaylor@aoc.nrao.edu>

G. B. Taylor (NRAO), D. A. Frail (NRAO) and S. R. Kulkarni (Caltech)
report:

"We have continued to monitor the four radio sources detected (GCN
308) within the RXTE/IPN localization (GCN 298) for GRB 990506. Some
time between May 8 and May 22 one of these sources dropped from 0.54
mJy at 8.4 GHz to below our detection limit (30-40 microJy), while the
rest remained constant. In order to confirm or reject the possibility
that this object is an Active Galactic Nucleus we initiated a
multi-frequency monitoring program.  We have recently analyzed the
data taken between May 22 and June 12 and found that the source
remains undetectable.  Our data lead us to conclude that an AGN
identification is unlikely, and that the transient source, hereafter
VLA J115450.1-2640.6, is the radio afterglow from GRB 990506.  VLA 
J115450.1-2640.6 was located at (J2000) R.A.= 11:54:50.14 (+/-0.04),
Dec.=-26:40:35.2 (+/-0.8). We urge all optical/IR observers to
re-investigate their images at this precise location for any sign of a
variable object."

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