Testing compact massive black hole binary candidates through multi-epoch spectroscopy

Abstract

Emission from two massive black holes (MBHs) bound in a close binary is expected to be modulated by different processes, such as the Doppler boost due to the orbital motion, accretion rate variability generated by the interaction with a circumbinary disc, and binary gravitational self-lensing. When the binary is compact enough, the two black holes are thought to be surrounded by a common broad-line region that reprocesses the impinging periodically varying ionising flux, creating broad emission lines with variable line shapes. Therefore, the study of broad emission line variability through multi-epoch spectroscopic campaigns is of paramount importance for the unambiguous identification of a binary. In this work, we study the response of a disc-like broad-line region to the Doppler-boosted ionising flux emitted by sub-milliparsec MBH binaries on a circular orbit and compare it with the response of a broad-line region illuminated by a single MBH with a periodically but isotropically varying intrinsic luminosity. We show that in the binary case, the time lags of the blue and red wings of the broad emission lines, arising from diametrically opposite sides of the circumbinary disc, are out of phase by half of the binary's orbital period, as they each respond to the periodic "lighthouse" modulation from the binary's continuum emission. This asymmetric time lag represents a new binary signature that cannot be mimicked by a single MBH.

13 pages, 16 figures

References in corpus (32)

• LSST: from Science Drivers to Reference Design and Anticipated Data Products
• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
• Are the Variations in Quasar Optical Flux Driven by Thermal Fluctuations?
• The Radius-Luminosity Relationship for Active Galactic Nuclei: The Effect of Host-Galaxy Starlight on Luminosity Measurements II. The Full Sample of Reverberation-Mapped AGNs
• The International Pulsar Timing Array: First Data Release
• A Compact Supermassive Binary Black Hole System
• An Eccentric Circumbinary Accretion Disk and the Detection of Binary Massive Black Holes
• False periodicities in quasar time-domain surveys
• The Quest for Dual and Binary Supermassive Black Holes: A Multi-Messenger View
• Hydrodynamics of circumbinary accretion: Angular momentum transfer and binary orbital evolution
• Limiting eccentricity of sub-parsec massive black hole binaries surrounded by self-gravitating gas discs
• Accretion-Driven Evolution of Black Holes: Eddington Ratios, Duty Cycles, and Active Galaxy Fractions
• Relativistic boost as the cause of periodicity in a massive black-hole binary candidate
• Evolution of the Nuclear Accretion Disk Emission in NGC 1097: Getting Closer to the Black Hole
• Quasi-periodicities at year-like timescales in Blazars
• Orbital Evolution of Equal-mass Eccentric Binaries due to a Gas Disk: Eccentric Inspirals and Circular Outspirals
• Equilibrium eccentricity of accreting binaries
• Double-peaked profiles: ubiquitous signatures of disks in the Broad Emission Lines of Active Galactic Nuclei
• Orbital Evolution of Binaries in Circumbinary Disks
• Shocks and angular momentum flips: a different path to feeding the nuclear regions of merging galaxies
• Alignment of supermassive black hole binary orbits and spins
• A Large Systematic Search for Close Supermassive Binary and Rapidly Recoiling Black Holes - II. Continued Spectroscopic Monitoring and Optical Flux Variability
• Ultra-Short-Period Massive Black Hole Binary Candidates in LSST as LISA "Verification Binaries"
• The orientation dependence of quasar single-epoch black hole mass scaling relationships
• Emission Signatures from Sub-parsec Binary Supermassive Black Holes I: Diagnostic Power of Broad Emission Lines
• Gravitational Self-Lensing in Populations of Massive Black Hole Binaries
• Emission Signatures from Sub-parsec Binary Supermassive Black Holes II: Effect of Accretion Disk Wind on Broad Emission Lines
• Lighthouse in the Dust: Infrared Echoes of Periodic Emission from Massive Black Hole Binaries
• ESPRESSO reveals a single but perturbed broad-line region in the supermassive black hole binary candidate PG 1302-102
• Constraining UV Continuum Slopes of Active Galactic Nuclei With CLOUDY Models of Broad Line Region EUV Emission Lines
• A fast test for the identification and confirmation of massive black hole binaries

Cited by in corpus (4)

• Hot, cold, and multi-component accretion flows around supermassive black hole binaries
• Identifying massive black hole binaries via light curve variability in optical time-domain surveys
• Can a time evolving, asymmetric broad line region mimic a massive black hole binary?
• Searching for unresolved massive black hole pairs through AGN photometric variability