An Interferometric Survey of the Areas Surrounding Four Intense Radio Sources

WE report here the results of an interferometric survey of the areas surrounding the intense radio sources Cassiopeia A, Cygnus A, Taurus A and Virgo A. These areas have remained unsurveyed because with most techniques the intense sources produce sidelobe responses which completely obscure any weaker ones surrounding them. Even with the aperture synthesis methods used in the 4C survey1 the grating responses obscure areas of several square degrees around the intense sources. The present search was conducted with a long baseline radio link interferometer which has the advantage that the sidelobe responses are reduced by several orders of magnitude because the intense sources are well resolved. This point is illustrated by Table 1 which lists the 408 MHz flux densities of the four intense sources together with the typical apparent flux densities as seen by the Jodrell Bank Mk III interferometer (32,000 wavelengths at 408 MHz).