Why Quasar Pairs are Binary Quasars and Not Gravitational Lenses

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Abstract
We use simple comparisons of the optical and radio properties of the wide separation (3''<Δθ<10'') quasar pairs to demonstrate that they are binary quasars rather than gravitational lenses. The most likely model is that all of the pairs are binary quasars, with a one-sided 2 σ (1 σ) upper limit of 22% (8%) on the lens fraction. Simple models for the expected enhancement of quasar activity during galaxy mergers that are consistent with the enhancement observed at low redshift can explain the incidence, separations, redshifts, velocity differences, and radio properties of the binary quasar population. Only a modest fraction (5%) of all quasar activity need be associated with galaxy mergers to explain the binary quasars.