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Astron. Astrophys. 329, 504-510 (1998)

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1. Introduction

The radio counterpart of the Galactic X-ray binary system Cygnus X-3 has been shown to display structure in its radio emission that appears to be "jet like", resembling emission from a central source. Interferometric observations reported by Geldzahler et al. (1983), Spencer et al. (1986) and Schalinski et al. (1995) imply the existence of this emission on a scale of tens of milliarcseconds. These observations are complicated by extreme scattering which is probably due to the presence of an electron screen near the source. The large scattering size, 16 mas at 6 cm wavelength, makes it difficult to image Cygnus X-3 due to the lack of short baselines (of order 50 to 300 km at 6 cm). During large outbursts, however, the intensity of the signal makes it possible to observe this source on longer baselines which are available on Very Long Baseline Interferometry (VLBI) networks such as the European VLBI Network (EVN).

A large outburst in the flux density of Cygnus X-3 was observed with the Green Bank interferometer at 13.3 and 3.6 cm in January, 1991. An adhoc VLBI experiment was organized using antennas of the EVN. Successful observations were obtained on January 24-27, 1991. We describe the results of these observations here.

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© European Southern Observatory (ESO) 1998

Online publication: December 8, 1997