2007MNRAS.377.1215Z

In this paper, we study the object SDSS J1130+0058 which is the only active galactic nuclei (AGN) known to have both double-peaked low-ionization broad emission lines and X-shaped radio structures. Emission from an accretion disc can reproduce the double-peaked line profile of broad Hα, but not the radio structure. Under the accretion disc model, the period of the inner emission-line region is about 230 yr. Using a new method to subtract the stellar component from the data of the Sloan Digital Sky Survey (SDSS) Data Release 4 (DR4), we obtain an internal reddening factor which is less than previously found. The implied smaller amount of dust disfavours the backflow model for the X-shaped radio structure. The presence of a binary black hole (BBH) system is the most natural way to explain both the optical and radio properties of this AGN. Under the assumption of the BBH model, we can estimate the BBH system has a separation of less than 0.04 pc with a period less than 59 yr; this may pose some problem to the emission-line region (BLR) sizes, still we conclude that the BBH model is favoured on the basis of the present limited information.