Warped accretion disks and quasars with episodic periodicity of long-term variations

TL;DR

This paper proposes a warped accretion disk model to explain quasi-periodic long-term optical variations in quasars, demonstrating that oscillating disk orientations can produce damped periodic light curves consistent with observations.

Contribution

It introduces a numerical model of warped accretion disks with free-bending waves to explain quasar variability, providing initial observational fitting evidence.

Findings

Simulated light curves exhibit damped periodicity matching observed features.

The model's fit to a quasar light curve yields a reduced chi-squared of approximately 2.4.

Warped disk oscillations can potentially explain long-term quasar variability.

Abstract

It has been found that some quasars are undergoing quasi-periodic variations (most of them with damped amplitudes) in optical bands from long-term monitoring campaigns, but how to explain the origin of such light curve variations still remains an open question. In this paper, we use the warped accretion disks model to explain the quasi-periodical variations. This model employs a free-bending wave traveling in an accretion disk which causes the orientation of the central part of the disk to oscillate from the line of sight, resulting in a quasi-periodical variation. We numerically solve the governing equation of warp propagation and calculate the simulated R-band light curves, finding that the periodical light curves generated by this model have damped amplitudes. To compare with observations, we select SDSSJ134820.42+194831.5 as a preliminary example from a sample of periodic quasar candidates by combining CRTS with other public survey data, and fitted its light curve with different observational angles. Our result gives a reduced $\chi^{2}\simeq 2.4$, implying that the model might give insights to future application of warped disk model.