SDSS J1130+0058 an X-shaped radio source with double-peaked low-ionization emission lines: a binary black hole system?

Abstract

In this paper we study the object SDSS J1130+0058 which is the only AGN known to have both double-peaked low-ionization broad emission lines, and also X-shaped radio structures. Emission from an accretion disk can reproduce the double-peaked line profile of broad H$\alpha$, but not the radio structure. Under the accretion disk model, the period of the inner emission line region is about 230 years. Using a new method to subtract the stellar component from the data of the SDSS DR4, we obtain an internal reddening factor which is less than previously found. The implied smaller amount of dust disfavors 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 ${\it both}$ 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 years, this may pose some problem to the BLRs sizes, still we conclude that the BBH model is favored on the basis of the present limited information.