We report the discovery of a small separation quasar pair ( z = 0.586 , O = 18.4 , 19.2 , sep. = 2 \farcs 3 ) associated with the radio source FIRST J164311.3+315618 ( S _ { 1400 } = 120 mJy ) .
The spectrum of the brighter quasar ( A ) has a much stronger narrow emission-line spectrum than the other ( B ) , and also stronger Balmer lines relative to the continuum .
The continuum ratio of the spectra is flat in the blue ( \lambda _ { obs } < 6000 Å ) at about 2.1 , but falls to 1.5 at longer wavelengths .
A K ^ { \prime } image shows two unresolved sources with a flux ratio of 1.3 .
The different colors appear to result from the contribution of the host galaxy of B , which is evident from Ca II and high-order Balmer absorption lines indicative of a substantial young stellar population .
New 3.6 cm VLA observations show that the compact radio source is coincident with quasar A ( B is only marginally detected ) .
We rule out the lensing hypothesis because the optical flux ratio is A/B \approx 1.5–2 while the radio flux ratio is A/B \gtrsim 40 , and conclude that this system is a binary .
Moreover , the radio-loud quasar is a compact steep spectrum source .
FIRST J164311.3+315618A , B is the lowest redshift and smallest separation binary quasar yet identified .