2017MNRAS.464.2203Z

In this paper, we study properties of the long-term optical variability of a large sample of 106 Sloan Digital Sky Survey (SDSS) spectroscopically confirmed active galactic nuclei (AGN) with double-peaked broad low-ionization emission lines (double-peaked emitters). The long-term optical light curves over 8 yr are collected from the Catalina Sky Surveys Data Release 2, and the Damped Random Walk (DRW) process is applied to describe the long-term variability of the double-peaked emitters. Meanwhile, the same DRW process is applied to long-term optical light curves of more than 7000 spectroscopically confirmed normal quasars in the SDSS Stripe82 Database. Then, we can find that the DRW process determined rest-frame intrinsic variability time-scales ln (τ/d) are about 5.8 and about 4.8 for the double-peaked emitters and for the normal quasars, respectively. The statistically longer intrinsic variability time-scales can be confirmed in the double-peaked emitters, after considerations of necessary effects, such as the effects from different distributions of redshift, black hole mass, and accretion rate between the double-peaked emitters and the normal quasars. Moreover, a radial dependence of the accretion rate {dot}m_R ∝ R^βwith larger values of β could be an acceptable interpretation of the longer intrinsic variability time-scales in the double-peaked emitters. Therefore, there are different intrinsic properties of emission regions between the double-peaked emitters and the normal quasars. The double-peaked emitters can be well treated as an unique subclass of AGN.