Distinguishing Tidal Disruption Events and Changing-look Active Galactic Nuclei via Variation in Mid-infrared Color

Abstract In this work, we propose that the time variation in mid-infrared (MIR) color is a promising probe to distinguish between MIR outbursts induced by tidal disruption events (TDEs) and changing-look active galactic nuclei (CLAGNs). With an optically selected sample containing TDEs, ambiguous nuclear transients (ANTs), and CLAGNs, we studied the variation in MIR color (W1 − W2) after subtracting the quiescent fluxes using NEOWISE-R data. The MIR color of TDEs and ANTs turns red faster than CLAGNs during the rising phase, as the color variation rate (CVR) of TDEs and ANTs is generally ≳0.2 mag yr −1 , whereas that of CLAGNs is generally ≲0.3 mag yr −1 . This may be caused by the difference between the ultraviolet light curves of TDEs/ANTs and CLAGNs, or be related to no or weak underlying AGN in TDEs/ANTs. In addition, TDEs have a redder color than ANTs at the earliest phase. Based on CVR, we selected high-probability TDE, ANT, and CLAGN candidates from MIR outbursts in samples of Jiang et al. and Masterson et al. We found that both samples are mixtures of TDEs/ANTs and CLAGNs. For MIR outbursts whose hosts are not Seyfert galaxies, we estimated that ∼50%–80% are TDEs and inferred a rate of infrared TDEs of 1.5–2.8 × 10 −5 galaxy −1 yr −1 , comparable with that of optical TDEs; the rest are CLAGNs, suggesting the presence of weak AGNs that cannot be identified using common diagnoses. Our work opens a new door for future classification of infrared-selected transients based on only photometric data.