Evidence for rapid disk formation and reprocessing in the X-ray bright tidal disruption event AT 2018fyk

Understand

We present optical spectroscopic and Swift UVOT/XRT observations of the X-ray and UV/optical bright tidal disruption event (TDE) AT 2018fyk/ASASSN-18ul discovered by ASAS-SN.

• The Swift lightcurve is atypical for a TDE, entering a plateau after $\sim$40 days of decline from peak.
• After 80 days the UV/optical lightcurve breaks again to decline further, while the X-ray emission becomes brighter and harder.
• In addition to broad H, He and potentially O/Fe lines, narrow emission lines emerge in the optical spectra during the plateau phase.