2022ApJ...936..132Y

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 (ω₀), 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 ω₀, 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.