Tidal disruption by extreme mass ratio binaries and application to ASASSN-15lh

Abstract

Tidal disruption events (TDEs) observed in massive galaxies with inferred central black hole masses $M_h > 10^8 \ M_\odot$ are presumptive candidates for TDEs by lower mass secondaries in binary systems. We use hydrodynamic simulations to quantify the characteristics of such TDEs, focusing on extreme mass ratio binaries and mpc separations where the debris stream samples the binary potential. The simulations are initialised with disruption trajectories from 3-body integrations of stars with parabolic orbits with respect to the binary center of mass. The most common outcome is found to be the formation of an unbound debris stream, with either weak late-time accretion or no accretion at all. A substantial fraction of streams remain bound, however, and these commonly yield structured fallback rate curves that exhibit multiple peaks or sharp drops. We apply our results to the superluminous supernova candidate ASASSN-15lh and show that its features, including its anomalous rebrightening at $\sim 100$ days after detection, are consistent with the tidal disruption of a star by a supermassive black hole in a binary system.