The double quasar 0957+561 as a gravitational lens: further VLA observations

Abstract

The twin quasars 0957+561 A,B, separated by only 6 arc s on the sky, have been shown to have nearly identical redshifts (z_e ≃ 1.41, z_a≃1.39) by Walsh et al.¹, who suggested that they were the double image of a single object, split by the gravitational refraction of an unseen massive intervening object. Further optical spectroscopy² has confirmed the remarkable similarities of the emission and absorption spectra of the two quasars, and strengthened the case for a gravitational lens model. Radio maps at 6 cm made with the Cambridge 5-km telescope³ and with the VLA⁴ showed that, in addition to two unresolved sources coincident with the optical quasars, there were extended regions of radio emission, apparently associated with the north (A) quasar which greatly complicated the gravitational lens hypothesis. We now report a full 12-h synthesis made at the VLA at 6-cm wavelength⁵ which confirmed the earlier maps and showed additional features at lower flux levels. In particular, this map revealed two small radio ‘jets’, one close to each of the quasars. The absence of corresponding second images of either of these jets near the other quasar was used to rule out models in which the gravitator was located near the midpoint of the line between A and B (ref. 5).