Long-term variability in the radio-quiet AGN Ark120

We compiled the historical archival photometric and spectroscopic data since 1974 and conducted a new two-year monitoring campaign in 2015-2017, resulting in a total temporal baseline over four decades. The long-term variations in the optical continuum exhibit a wave-like pattern and the H{beta} integrated flux series varies with a similar behavior.

The broad H{beta} profiles have asymmetric double peaks, which change strongly with time and tend to merge into a single peak during some epochs. The period in the optical continuum determined from various period-search methods is about 20yr, and the estimated false alarm probability with null hypothesis simulations is about 1x10^-3^. The overall variations of the broad H{beta} profiles also follow the same period.