Examining AGN UV/optical Variability Beyond the Simple Damped Random Walk

Understand

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 (CARMA) process, which can be fully described using four independent parameters: a natural oscillation frequency ($\omega_{0}$), a damping ratio ($\xi$), a characteristic perturbation timescale ($\tau_{\mathrm{perturb}}$), and an amplitude for the perturbing white noise ($\sigma_{\mathrm{\epsilon}}$).
• The asymptotic variability amplitude of a DHO process is quantified by $\sigma_{\mathrm{DHO}}$ -- a function of $\omega_{0}$, $\xi$, $\tau_{\mathrm{perturb}}$, and $\sigma_{\mathrm{\epsilon}}$.
• We find that both $\tau_{\mathrm{perturb}}$ and $\sigma_{\mathrm{\epsilon}}$ follow different dependencies with rest-frame wavelength ($\lambda_{\mathrm{RF}}$) on either side of 2500 \AA, whereas $\sigma_{\mathrm{DHO}}$ follows a single power-law relation with $\lambda_{\mathrm{RF}}$.