Dormancy and Reawakening Over Years: Eight New Recurrent Changing-Look AGNs

TL;DR

This study reports the discovery of eight new recurrent changing-look AGNs, revealing that some AGNs can undergo dormancy and reactivation within a few years, offering insights into their episodic accretion behavior.

Contribution

The paper presents eight newly identified recurrent changing-look AGNs, doubling the known sample and providing detailed analysis of their long-term variability and accretion state transitions.

Findings

Many AGNs exhibit 4-7 year prolonged dim states.

Turn-on and turn-off timescales are similar, consistent with disk instability models.

Transitions are driven by accretion disk emission changes, not dust obscuration.

Abstract

We report the discovery of eight new recurrent changing-look (CL) active galactic nuclei (AGNs), including seven re-brightening turn-off AGNs and one fading turn-on AGN. These systems are valuable for placing constraints on the duration of dim and bright states, which may be linked to the AGN duty cycle or disk instability. Long-term optical light curve analysis reveals that many objects in our sample exhibit a prolonged plateau during the dim states lasting 4 to 7 years, with gradual turn-on/off process. We observe no significant difference between the turn-on and turn-off timescales, and this timescale is broadly consistent with the heating/cooling front propagation timescale. The comparison between optical and infrared variations supports that these transitions are driven by changes in accretion disk emission rather than dust obscuration. Our discovery significantly increases the previously identified recurrent CL AGN sample from eleven objects to nineteen, demonstrating that some AGNs can enter dormancy and reawaken on timescales of a few years, which provides useful information for understanding AGN episodic accretion.