Effects of intrinsic AGN variability on optical QPOs related to sub-pc binary black hole systems in broad line AGN

Abstract

In this manuscript, an oversimplified model is proposed to test the effects of intrinsic AGN variability on expected optical quasi-periodic oscillations (QPOs) related to sub-pc binary black hole systems (BBHs) in broad line AGN. The commonly accepted CAR (Continuous AutoRegressive) process is applied to describe intrinsic AGN variability related to each BH accreting system in a sub-pc BBH system. Considering obscurations related to orbital rotations with periodicity $T_p$, artificial light curves including signals for optical QPOs can be built. Then, comparing the intrinsic periodicities $T_p$ with the measured robust periodicities $T_o$ through the artificial light curves, distributions of $T_p/T_o$ have four significant peaks around 1, 2, 3 and 4, leading less than half of the artificial light curves to have consistency between $T_o$ and $T_p$. Moreover, different collected model parameters have few effects on the distributions of $T_p/T_o$, indicating the effects of intrinsic AGN variability on optical QPOs are significantly strong and stable. Furthermore, after checking properties of optical QPOs in the light curves with different time steps, there are tiny effects of time steps on optical QPOs.