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GCN Circular 374

GRB990704 radio and optical observations
1999-07-06T19:26:40Z (25 years ago)
Paul Vreeswijk at U of Amsterdam <>
E. Rol, P. Vreeswijk, T. Galama (U. of Amsterdam), N. Masetti,
E. Palazzi, E. Pian, F. Frontera (ITESRE, CNR, Bologna), J. van
Paradijs (U. of Amsterdam and U. of Alabama in Huntsville),
C. Kouveliotou (USRA/MSFC), R. Strom (NFRA and U. of Amsterdam), G. de
Bruyn (NFRA and U. of Groningen) and T. Augusteijn (ESO) report:

We have observed the BeppoSAX NFI error circle of GRB 990704 (Gandolfi
1999, GCN 364) with the Westerbork Synthesis Radio Telescope (WSRT).
We observed for 9.2 hours at 4.88 GHz centered on July 5.75 UT, 1999.
Within the error circle we detect two sources at 4.88 GHz. Their
fluxes and positions are given below:

	flux (mJy)	RA(J2000)	Decl.(J2000)

	 0.68		12:19:27.2	-03:51:38.5
	 0.35		12:19:31.0	-03:52:05.3

The error in the flux is 0.065 mJy. The error in the RA and Decl. are
0.5" and 5", respectively.

We have also observed the error circle in the R band with the ESO 2.2m
(La Silla) and VLT-UT1 Antu (Paranal) telescopes, 6.5 and 30.5 hours
after the burst, respectively. We calibrated these images with the
Landolt SA104 field (stars 350 and 456; Landolt 1992, AJ, 104, 340).
We detect an object at RA 12:19:27.20, Decl. -3:51:39.7 (J2000;
positional accuracy of about 2"), coincident with the first radio

We measure the following magnitudes for this object:

        UT Date         R       err.      telescope
        July 4.96       22.05   0.16      2.2m
        July 6.01       22.00   0.05      VLT-UT1
        July 6.07       21.87   0.07      VLT-UT1

The error in the absolute calibration (estimated to be 0.2 mag.) is
not included in the error listed above. The object is constant within
the measurement errors and it is therefore not likely the counterpart
of GRB990704.

At the position of the second radio source, no object is detected. The
5 sigma limiting magnitudes of the 2.2m and the co-added VLT-UT1
images are R=22.2 and R=23.5, respectively.

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