Systematic Classification of Tidal Disruption Event Light Curves from the Zwicky Transient Facility

Tidal disruption events (TDEs) happen when a star comes close enough to a black hole for the black hole’s tidal forces to rip apart the star into a stream of debris, roughly half of which falls back onto the black hole and is accreted, resulting in a luminous flare of radiation. We present the analysis of the optical (g and r band) light curves of a sample of over two dozen TDEs detected by the Zwicky Transient Facility (ZTF). This TDE sample is one of the few of its size and quality. We performed both visual analysis and quantitative fitting of the TDE light curves, resulting in measurements of the timescales for the rise, peak, and decay of each light curve. We searched for relationships between these timescales and the TDEs’ host galaxy masses, but did not find any strong correlations. A simple power law decay (t^-5/3) from peak brightness is traditionally expected from the light curves of TDEs. However, our analysis revealed detailed substructures and other features in the light curves’ decays from peak that strongly deviate from the expected power law. We therefore designed a TDE optical light curve shape classification system with three classifications — Power law (TDE-P), Plateau (TDE-Pl), and Structured (TDE-S) — in order to categorize the various shapes and features we found in the TDE light curve decays. We believe that exploring optical TDE light curve shapes and decay timescales through the perspective of the proposed classification system may provide new insights into understanding the physical mechanisms that produce optical emission in TDEs and drive their light curve shape. This project was supported in part by the NSF REU grant AST-1757321 and by the Nantucket Maria Mitchell Association.