Tidal disruptions in circumbinary disks. II: Observational signatures in the reverberation spectra

Abstract

Supermassive Binary Black Holes (SMBBHs) with sub-pc separations form in the course of galaxy mergers, if both galaxies harbour massive black holes. Clear observational evidence for them however still eludes us. We propose a novel method of identifying these systems by means of reverberation mapping their circumbinary disk after a tidal disruption event has ionized it. The tidal disruption of a star at the secondary leads to strong asymmetries in the disk response. We model the shape of the velocity--delay maps for various toy disk models and more realistic gas distributions obtained by SPH simulations. The emissivity of the ionized disk is calculated with {\em Cloudy}. We find peculiar asymmetries in the maps for off center ionizing sources that may help us constrain geometrical parameters of a circumbinary disk such as semi-major axis and orbital phase of the secondary, as well as help strengthen the observational evidence for sub-parsec SMBBHs as such.