THE PECULIAR OPTICAL SPECTRUM OF 4C+22.25: IMPRINT OF A MASSIVE BLACK HOLE BINARY?

We report the discovery of peculiar features in the optical spectrum of 4C+22.25, a flat spectrum radio quasar at z = 0.4183 observed in the Sloan Digital Sky Survey and in a dedicated spectroscopic follow-up from the Nordic Optical Telescope. The H beta and H alpha lines show broad profiles (FWHM similar to 12,000 km s(-1)), faint fluxes, and extreme offsets (Delta v = 8700 +/- 1300 km s(-1)) with respect to the narrow emission lines. These features show no significant variation in a time lag of similar to 3.1 yr (rest frame). We rule out possible interpretations based on the superposition of two sources or on recoiling black holes, and discuss the virtues and limitations of a massive black hole binary scenario.