Warped Accretion Disks and Quasars with Episodic Periodicity of Long-term Variations

Abstract It has been found from long-term monitoring campaigns that some quasars are undergoing quasiperiodic variations (most of them with damped amplitudes) in optical bands, 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 quasiperiodical 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 quasiperiodical 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 fitting its light curve with different observational angles. Our result gives a reduced χ 2 ≃ 2.4, implying that the model might give insights into the future application of the warped disk model.