Tests for Standard Accretion Disk Models by Variability in Active Galactic Nuclei

TLDR: In this paper, the standard accretion disk models of active galactic nuclei (AGNs) are tested using light curves of 26 objects that have been well observed using reverberation mapping.

Abstract: In this paper, standard accretion disk models of active galactic nuclei (AGNs) are tested using light curves of 26 objects that have been well observed using reverberation mapping. Timescales of variations are estimated by the most common definition of the variability timescale and the zero-crossing time of the autocorrelation function of the optical light curves for each source. The timescales of variations measured by the two methods are consistent with each other. If the typical value of the viscosity parameter alpha similar to 0.1 is adopted, the measured optical variability timescales are closest to the thermal timescales of the standard disks. If alpha is allowed to range from similar to 0.03 to similar to 0.2, the measured timescales are consistent with the thermal timescales of the standard disks. There is a linear relation between the measured variability timescales and black hole masses; this linear relation is qualitatively consistent with expectation of the standard accretion disk models. The time lags measured by the z-transformed discrete correlation function (ZDCF) between different bands are on the order of days. The measured time lags of NGC 4151 and NGC 7469 are marginally consistent with the time lags estimated in the case of continuum thermal reprocessing for the standard accretion disk models. However, the measured time lags of NGC 5548 and Fairall 9 are unlikely to be the case of continuum thermal reprocessing. Our results are unlikely to be inconsistent with, or are likely to be conditionally in favor of, the standard accretion disk models of AGNs.