Cause of the imbalance between transition sequences in RCL AGNs

Ascertain whether the observed predominance of turn-off followed by turn-on transitions among recurrent changing-look active galactic nuclei is primarily driven by longer temporal monitoring baselines for turn-off sources or reflects intrinsic physical differences and/or selection effects between the two transition sequences.

Background

Within the identified sample, 21 objects undergo a turn-off followed by a turn-on transition, while only four display the reverse sequence. The authors evaluate spectroscopic sampling and report longer median maximum separations for turn-off sources, suggesting an observational-bias explanation.

Nevertheless, they explicitly state they cannot rule out intrinsic differences or selection effects as contributing factors, and note that with an unbiased and sufficiently long baseline, the two transition types are expected to be roughly comparable.