ABSTRACT. Supermassive black hole binaries (SMBHBs) are products of galaxy mergers, and are important in testing Λ cold dark matter cosmology and locating gravitational-wave-radiation sources. A unique electromagnetic signature of SMBHBs in galactic nuclei is essential in identifying the binaries in observations from the IR band through optical to X-ray. Recently, the flares in optical, UV, and X-ray caused by supermassive black holes (SMBHs) tidally disrupting nearby stars have been successfully used to observationally probe single SMBHs in normal galaxies. In this Letter, we investigate the accretion of the gaseous debris of a tidally disrupted star by a SMBHB. Using both stability analysis of three-body systems and numerical scattering experiments, we show that the accretion of stellar debris gas, which initially decays with time t ^–5/3, would stop at a time T _tr ηT _b. Here, η ~ 0.25 and T _b is the orbital period of the SMBHB. After a period of interruption, the accretion recurs discretely at time T _r ξT _b, where ξ ~ 1. Both η and ξ sensitively depend on the orbital parameters of the tidally disrupted star at the tidal radius and the orbit eccentricity of SMBHB. The interrupted accretion of the stellar debris gas gives rise to an interrupted tidal flare, which could be used to identify SMBHBs in non-active galaxies in the upcoming transient surveys.

Key words: accretion, accretion disks; black hole physics; galaxies: active; galaxies: evolution; galaxies: nuclei; gravitational waves

Print publication: Issue 1 (2009 November 20)
Received 2009 August 31, accepted for publication 2009 October 20
Published 2009 November 3