The peculiar optical spectrum of 4C+22.25: Imprint of a massive black hole binary?
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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 SDSS
and in a dedicated spectroscopic follow-up from the Nordic Optical
Telescope. The Hbeta and Halpha lines show broad profiles (FWHM~12,000
km/s), faint fluxes and extreme offsets (Delta v=8,700+/-1,300 km/s)
with respect to the narrow emission lines. These features show no
significant variation in a time lag of ~3.1 yr (rest frame). We rule out
possible interpretations based on the superposition of two sources or on
recoiling black holes, and we discuss the virtues and limitations of a
massive black hole binary scenario.