VLA Observations of the Double Quasar 0957+561: Gravitational Double Image or Binary Quasar?

Extract

The radio source 0957+561 was identified by Walsh et al. (1979, Nature 279, pp.381–384) with a pair of quasars, 6.1 apart on the sky, whose optical emission and absorption spectra are nearly identical. Walsh et al. suggested a gravitational lens interpretation in which a single object is split into two images by an intervening massive object. Using the Very Large Array of the NRAO we have made a 6-cm wavelength radio map of 0957+561. The map shows unresolved sources of 36 and 30 mJy coincident with the optical N and S quasars, and a complex extended source of ~130 mJy (Roberts, Greenfield, and Burke: 1979, Science August 31). The extended emission lies on an arc containing the N quasar, and consists of two resolved sources containing 75 and 28 mJy, located 5.8 and 5.6 NE of the N quasar, a weak source of ~10 mJy about 5.5 SW of the N quasar, and a suggestion of a bridge connecting the NE and SW sources and the N quasar. There is no evidence of radio emission from a massive object between the two quasars. Although the existence of the extended source does not rule out a gravitational lens model for 0957+561, the underlying source required would have an unusual morphology. In addition, if the refracting object is at the redshift of the absorption seen in both quasars, its mass would have to be at least 2 × 10¹⁴ solar masses. Further observations at the VLA could rule out the gravitational lens model for 0957+561 if a second image corresponding to the NE extended component is not found.