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

TL;DR

This paper proposes a novel reverberation mapping method to identify supermassive binary black holes by analyzing asymmetries in the ionized circumbinary disk's spectra after a tidal disruption event.

Contribution

It introduces a new observational technique using reverberation mapping and models the spectral response to detect sub-parsec supermassive binary black holes.

Findings

Asymmetries in velocity--delay maps can reveal binary parameters.

Modeling shows potential to constrain orbital phase and semi-major axis.

Method enhances prospects for observational evidence of SMBBHs.

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.