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Velocity offsets in the broad Balmer lines of quasars and their temporal variations serve as indirect evidence for bound supermassive black hole binaries (SBHBs) at sub-parsec separations. In this work, we test the SBHB hypothesis for 14 quasars with double-peaked broad emission lines using their long-term (14–41 yr) radial velocity curves. We improve on the previous work by (i) using elliptical instead of circular orbits for the SBHBs, (ii) adopting a statistical model for radial velocity jitter, (iii) employing a Markov chain Monte Carlo method to explore the orbital parameter space efficiently and build posterior distributions of physical parameters, and (iv) incorporating new observations. We determine empirically that jitter comprises approximately Gaussian distributed fluctuations about the smooth radial velocity curves that are larger than the measurement errors by factors of a few. We initially treat jitter by enlarging the effective error bars and then verify this approach via a variety of Gaussian process models for it. We find lower mass limits for the hypothesized SBHBs in the range 108–1011 M⊙. For seven objects, the SBHB scenario appears unlikely based on goodness-of-fit tests. For two additional objects, the minimum SBHB masses are unreasonably large (>1010 M⊙), strongly disfavouring the SBHB scenario. Using constraints on the orbital inclination angle (which requires some assumptions) makes the minimum masses of four more objects unreasonably large. We also cite physical and observational arguments against the SBHB hypothesis for nine objects. We conclude that the SBHB explanation is not the favoured explanation of double-peaked broad emission lines. [ABSTRACT FROM AUTHOR]

We present observations of the double-peaked broad Hα profile emitted by the active nucleus of NGC7213 using the Gemini South Telescope in 13 epochs between 2011 September 27 and 2013 July 23. This is the first time that the double-peaked line profile of this nucleus - typical of gas emission from the outer parts of an accretion disc surrounding a supermassive black hole (SMBH) - is reported to vary. From the analysis of the line profiles we find two variability time-scales: (1) the shortest one, between 7 and 28 d, is consistent with the light travel time between the ionizing source and the part of the disc emitting the line; and (2) a longer one of≥3m corresponding to variations in the relative intensity of the blue and red sides of the profile, which can be identified with the dynamical time-scale of this outer part of the accretion disc. We modelled the line profiles as due to emission from a region between ≈300 and 3000 gravitational radii of a relativistic, Keplerian accretion disc surrounding the SMBH. Superposed on the disc emissivity, the model includes an asymmetric feature in the shape of a spiral arm with a rotation period of ≈21 m, which reproduces the variations in the relative intensity of the blue and red sides of the profile. Besides these variations, the rms variation profile reveals the presence of another variable component in the broad line, with smaller velocity width W68 (the width of the profile corresponding to 68 per cent of the flux) of∼2100 km s-1. [ABSTRACT FROM AUTHOR]