Recurrent outbursts in the broad-line region of NGC 1566

The authors have used data obtained over a period of 15 yr to study the variations of the broad Hα and Hβ emission in the active galactic nucleus of NGC 1566. Four periods of activity are detected. Each lasts for ≡1300 days. The quiescent phase between two consecutive active periods has a duration from a few months to a year. The AGN remains in its highest state for a rather short time, certainly less than a month. The most recent period of activity is characterized by a series of rapid bursts. A single burst has a typical rise time of 20 days and an exponential decay of ≡400 days. Constraints on possible energy sources for the outbursts are discussed.