Differential Interferometric Signatures of Close Binaries of Supermassive Black Holes in Active Galactic Nuclei: II. Merged Broad Line Regions

Abstract

Pairs of supermassive black holes (SMBHs) at different stages are natural results of galaxy mergers in the hierarchical framework of galaxy formation and evolution. However, identifications of close binaries of SMBHs (CB-SMBHs) with sub-parsec separations in observations are still elusive. Recently, unprecedented spatial resolutions achieved by GRAVITY/GRAVITY+ onboard The Very Large Telescope Interferometer through spectroastrometry (SA) provide new opportunities to resolve CB-SMBHs. Differential phase curves of CB-SMBHs with two independent broad-line regions (BLRs) are found to have distinguished characteristic structures from a single BLR \citep{songsheng2019}. Once the CB-SMBH evolves to the stage where BLRs merge to form a circumbinary BLR, it will hopefully be resolved by the pulsar timing array (PTA) in the near future as sources of nano-hertz gravitational waves. In this work, we use a parameterized model for circumbinary BLRs to calculate line profiles and differential phase curves for SA observations. We show that both profiles and phase curves exhibit asymmetries caused by the Doppler boosting effect of accretion disks around individual black holes, depending on the orbital parameters of the binary and geometries of the BLR. We also generate mock SA data using the model and then recover orbital parameters by fitting the mock data. Degeneracies between parameters contribute greatly to uncertainties of parameters but can be eased through joint analysis of multiple-epoch SA observations and reverberation mappings.

21 pages, 17 figures, accepted by ApJ

References in corpus (21)

• Gravitational-wave sensitivity curves
• The Evolution of Galaxy Structure over Cosmic Time
• A Compact Supermassive Binary Black Hole System
• Massive black hole binary mergers within sub-pc scale gas discs
• Kinematics of Parsec-Scale Jets of Gamma-Ray Blazars at 43~GHz within the VLBA-BU-BLAZAR Program
• Upper bounds on the low-frequency stochastic gravitational wave background from pulsar timing observations: current limits and future prospects
• The International Pulsar Timing Array second data release: Search for an isotropic Gravitational Wave Background
• Gravitational waves from resolvable massive black hole binary systems and observations with Pulsar Timing Arrays
• Reverberation Measurements of the Inner Radius of the Dust Torus in 17 Seyfert Galaxies
• Modeling reverberation mapping data I: improved geometric and dynamical models and comparison with cross-correlation results
• FIRST `Winged' and `X'-shaped Radio Source Candidates
• The First Spectroscopically Resolved Sub-parsec Orbit of a Supermassive Binary Black Hole
• The central parsec of NGC 3783: a rotating broad emission line region, asymmetric hot dust structure, and compact coronal line region
• Reverberation Mapping of the Broad-line Region in NGC 5548: Evidence for Radiation Pressure?
• Multi-messenger Time-domain Signatures Of Supermassive Black Hole Binaries
• Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei. II. Atlas of two-dimensional transfer functions
• Kinematic signatures of reverberation mapping of close binaries of supermassive black holes in active galactic nuclei III. The case of elliptical orbits
• Variation of Broad Emission Lines from QSOs with Optical/UV Periodicity to Test the Interpretation of Supermassive Binary Black Holes
• Measuring black hole mass of type I active galactic nuclei by spectropolarimetry
• Spiral Arms in Broad-line Regions of Active Galactic Nuclei. I. Reverberation and Differential Interferometric Signals of Tightly Wound Cases
• Spectroastrometric Reverberation Mapping of Broad-line Regions

Cited by in corpus (3)

• Unveiling the solution to the final-parsec problem by combining milli-Hertz gravitational-wave observation and AGN survey
• Probing $H_0$ and resolving AGN disks with ultrafast photon counters
• On Variation of Light Curves and Broad Emission Lines for Periodic QSOs from co-rotating Supermassive binary black holes in elliptical orbits