The quasar Q2345+-007A, B - A case for the double gravitational lens?

Abstract

The recently reported double quasar Q2345+007A, B, with a large separation of about 7.3 arcsec between its components, is demonstrated to impose stringent constraints on possible gravitational lens models. A single gravitational lens can produce the large separation only if it is placed close to the observer at a redshift Z ≲ 0.14. A model involving two intervening galaxies at different redshifts (the double lens) is studied and shown to account for the observed features with reasonable values for the lens parameters. The effects of a cluster are also considered in some detail. Observational tests for distinguishing between various scenarios are suggested; in particular, the time delay between the two images turns out to have opposite signs for the single lens and double lens models.