Letter to the Editor

Time-dependent obscuration of a tidal disruption event candidate in the active galactic nucleus CSS100217

Guangxi Key Laboratory for Relativistic Astrophysics, School of Physical Science and Technology, Guangxi University, Nanning 530004, China

^⋆ Corresponding authors: xgzhang@gxu.edu.cn; lew@gxu.edu.cn

Received: 2 August 2025
Accepted: 16 September 2025

Abstract

CSS100217 is considered a peculiar tidal disruption event (TDE) candidate occurring in an active galactic nucleus (AGN). Unlike typical TDEs, for which the post-flare luminosity is equal to that pre-flare, CSS100217 decayed to ∼0.4 magnitudes fainter than its pre-flare V band level. In this manuscript, we propose an obscured TDE model to explain the light curve of CSS100217. Assuming that the time-dependent obscuration, caused by the TDE unbound stellar debris, or by nuclear clouds moving around the supermassive black hole (SMBH), follows a Weibull distribution, we find that the light curve of CSS100217 can be described by the tidal disruption of a 4.6_−0.9^+0.9 M_⊙ main-sequence star by a 3.3_−0.3^+0.3 ×10⁷ M_⊙ black hole. The total energy of the event derived from our fit is 7.23 × 10⁵³ ergs and about 1.38 M_⊙ of debris mass is accreted by the central SMBH. The model indicates that the contribution of the host galaxy to the observed pre-flare optical luminosity is not-significant compared to that of the AGN, which is consistent with the results of the spectral analysis. These results suggest that obscuration may play an important role in explaining the unusual TDE-like variability observed in CSS100217.