Examining AGN UV/Optical Variability beyond the Simple Damped Random Walk

We present damped harmonic oscillator (DHO) light-curve modeling for a sample of 12,714 spectroscopically confirmed quasars in the Sloan Digital Sky Survey Stripe 82 region. DHO is a second-order continuous-time autoregressive moving-average process, which can be fully described using four independent parameters: a natural oscillation frequency (ω ₀), a damping ratio (ξ), a characteristic perturbation timescale (τ _perturb), and an amplitude for the perturbing white noise (σ _ϵ ). The asymptotic variability amplitude of a DHO process is quantified by σ _DHO-a function of ω ₀, ξ, τ _perturb, and σ _ϵ . We find that both τ _perturb and σ _ϵ follow different dependencies with rest-frame wavelength (λ _RF) on either side of 2500 Å, whereas σ _DHO follows a single power-law relation with λ _RF. After correcting for wavelength dependence, σ _DHO exhibits anticorrelations with both the Eddington ratio and the black hole mass, while τ _perturb-with a typical value of days in the rest frame-shows an anticorrelation with the bolometric luminosity. Modeling active galactic nuclei (AGN) variability as a DHO offers more insight into the workings of accretion disks close to the supermassive black holes at the center of AGN. The newly discovered short-term variability (characterized by τ _perturb and σ _ϵ ) and its correlation with bolometric luminosity pave the way for new algorithms that will derive fundamental properties (e.g., Eddington ratio) of AGN using photometric data alone.