TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  491
SUBJECT: GRB991216 radio observations
DATE:    99/12/18 17:54:34 GMT
FROM:    Evert Rol at U.Amsterdam  <evert@astro.uva.nl>

E. Rol, P.M. Vreeswijk (U. of Amsterdam), R. Strom (NFRA, U. of
Amsterdam), C. Kouveliotou (USRA, NASA/MSFC), E. Pian (ITESRE,
Bologna), A. Castro-Tirado (LAEFF-INTA, Madrid), J. Hjorth (U. of
Copenhagen) and J. Greiner (AIP, Potsdam) report on behalf of a larger
European collaboration:

"We have performed observations with the Westerbork Synthesis Radio
Telescope (WSRT) at the position of the optical counterpart of
GRB991216 (Uglesich et al., GCN 472), on Dec. 17 and 18 at 4.8 GHz and
1.4 GHz, for 6 hours at each frequency.
At 4.8 GHz, we detect a 6 sigma radio source, coincident with the
position of the radio afterglow reported by Taylor et al. (GCN 483)
and by Pooley (GCN 489). At 1.4 GHz, we do not detect anything at this
position, with an rms upper limit of 0.17 mJy. This upper limit can be
reduced further.

If we split the observation into four epochs, we detect significant
variability of the flux intensity of the source at 4.8 GHz, as can be
seen from the following table:

UT Dec 1999	flux (mJy)	sigma (mJy)
(mid obs.)
17.783		0.82		0.13
17.997		0.84		0.13
18.044		1.62		0.13
18.153		0.70		0.16
"

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