Tidal disruption events in active galactic nuclei

TL;DR

This paper investigates how tidal disruption events in active galactic nuclei interact with accretion disks, affecting their evolution, luminosity, and emission spectra through simulations of stream-disk collisions.

Contribution

It provides the first detailed simulations of stream-disk collisions in AGNs, revealing complex shock dynamics, energy dissipation, and potential observational signatures of TDEs in active galactic nuclei.

Findings

Collision excites shocks leading to high energy dissipation.

Much of the radiation is trapped and advected into the black hole.

The emergent spectrum may differ from typical TDE or AGN spectra.

Abstract

A fraction of tidal disruption events (TDEs) occur in active galactic nuclei (AGNs) whose black holes possess accretion disks; these TDEs can be confused with common AGN flares. The disruption itself is unaffected by the disk, but the evolution of the bound debris stream is modified by its collision with the disk when it returns to pericenter. The outcome of the collision is largely determined by the ratio of the stream mass current to the azimuthal mass current of the disk rotating underneath the stream footprint, which in turn depends on the mass and luminosity of the AGN. To characterize TDEs in AGNs, we simulated a suite of stream--disk collisions with various mass current ratios. The collision excites shocks in the disk, leading to inflow and energy dissipation orders of magnitude above Eddington; however, much of the radiation is trapped in the inflow and advected into the black hole, so the actual bolometric luminosity may be closer to Eddington. The emergent spectrum may not be thermal, TDE-like, or AGN-like. The rapid inflow causes the disk interior to the impact point to be depleted within a fraction of the mass return time. If the stream is heavy enough to penetrate the disk, part of the outgoing material eventually hits the disk again, dissipating its kinetic energy in the second collision; another part becomes unbound, emitting synchrotron radiation as it shocks with surrounding gas.