Discovery of a probable binary quasar

The discovery of an apparent quasar pair associated with radio source PKS 1145-071 is reported. The observations comprise B and V CCD images obtained at the 2.2-m telescope at ESO on December 29, 1986, 320-700-nm spectra obtained with a reticon spectrograph at the MMT on January 3-4, 1987, and radio maps (primarily at 2 cm) obtained with the C configuration of the VLA on January 9, 1987; the data are presented graphically and characterized in detail. Findings reported from the optical observations include redshift 1.345, separation 4.2 arcsec in projection, optical intensity ratio 2.5, and rest-frame redshift difference 250 + or - 100 km/s (in the strong C IV line) or 100 + or - 100 km/s (without this line) - consistent with zero. However, the fainter component is fainter by a factor of at least 500 at 2 cm than in the visible; from this it is inferred that the objects constitute a true binary quasar with a total mass of at least (10 to the 11th)/h solar mass.