TESS shines light on the origin of the ambiguous nuclear transient ASASSN-18el. Issue 3 (16th March 2023)

• Record Type: Journal Article
• Authors: Hinkle, Jason T; Kochanek, Christopher S; Shappee, Benjamin J; Vallely, Patrick J; Auchettl, Katie; Fausnaugh, Michael; Holoien, Thomas W-S; Treiber, Helena P; Payne, Anna V; Gaudi, B Scott; Stassun, Keivan G; Thompson, Todd A; Tonry, J L; Villanueva, Steven
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 521:Issue 3(2023)
• Page Start: 3517
• Page End: 3526
• Publication Date: 2023-03-16
• Subjects: accretion, accretion discs -- black hole physics -- galaxies: active -- galaxies: nuclei; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stad746
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We analyse high-cadence data from the Transiting Exoplanet Survey Satellite ( TESS ) of the ambiguous nuclear transient (ANT) ASASSN-18el. The optical changing-look phenomenon in ASASSN-18el has been argued to be due to either a drastic change in the accretion rate of the existing active galactic nucleus (AGN) or the result of a tidal disruption event (TDE). Throughout the TESS observations, short-time-scale stochastic variability is seen, consistent with an AGN. We are able to fit the TESS light curve with a damped-random-walk (DRW) model and recover a rest-frame variability amplitude of $\hat{\sigma } = 0.93 \pm 0.02$ mJy and a rest-frame time-scale of $\tau _{DRW} = 20^{+15}_{-6}$ d. We find that the estimated τ DRW for ASASSN-18el is broadly consistent with an apparent relationship between the DRW time-scale and central supermassive black hole mass. The large-amplitude stochastic variability of ASASSN-18el, particularly during late stages of the flare, suggests that the origin of this ANT is likely due to extreme AGN activity rather than a TDE.