Dormancy and Reawakening over Years: Eight New Recurrent Changing-look AGNs

Abstract

We report the discovery of eight new recurrent changing-look (CL) active galactic nuclei (AGNs), consisting of seven rebrightening 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 analysis of optical light curves reveals that many objects in our sample exhibit a prolonged plateau during the dim states lasting 5–7 yr, with a 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 propagation timescale for the heating/cooling front. Comparison between the optical and infrared variations supports the idea 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, demonstrating that some AGNs can enter dormancy and reawaken on timescales of a few years, which provides useful information for understanding episodic AGN accretion.

Keywords

• Active galactic nuclei
• Quasars