Dissecting the nanoHz gravitational wave sky: frequency-correlated anisotropy induced by eccentric supermassive black hole binaries

Abstract

Revealing the nature of the nanoHz gravitational wave (GW) signal recently reported by Pulsar Timing Arrays (PTAs) collaborations around the world is the next goal of low-frequency GW astronomy. The signal likely originates from the incoherent superposition of GWs emitted by a cosmological population of supermassive black hole binaries (SMBHBs). Those binaries can be highly eccentric and/or strongly coupled to their nuclear environment, resulting in an attenuation of the overall GW signal at low frequencies. In this paper, we propose to use the correlation properties of the distributed GW power in the sky across the frequency spectrum as a smoking gun for eccentric SMBHBs thus allowing to break the spectral degeneracy between eccentricity and environmental effect. The simple underlying idea is that, contrary to circular binaries, eccentric ones emit a broadband spectrum thus resulting in similar sky maps at different frequencies. We first demonstrate the applicability of this simple concept on sky maps constructed directly from the theoretical sky distribution of the GWB power induced by realistic populations of SMBHBs. We then demonstrate the viability of this analysis on simulated SKA-like PTA data. By statistically comparing sky maps reconstructed from hundreds injected circular and highly eccentric SMBHB populations, we find that eccentricity can be detected at $3\sigma$ in more than $50\%$ of cases.

12 pages, 8 figures, submitted to A&A

References in corpus (32)

• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array
• The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
• Tempo2, a new pulsar timing package. II: The timing model and precision estimates
• The stochastic gravitational-wave background from massive black hole binary systems: implications for observations with Pulsar Timing Arrays
• Gravitational waves from resolvable massive black hole binary systems and observations with Pulsar Timing Arrays
• Expected properties of the first gravitational wave signal detected with pulsar timing arrays
• Interaction of massive black hole binaries with their stellar environment: I. Ejection of hypervelocity stars
• Relating gravitational wave constraints from primordial nucleosynthesis, pulsar timing, laser interferometers, and the CMB: implications for the early universe
• On measuring the gravitational-wave background using Pulsar Timing Arrays
• The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries
• The NANOGrav 15-year Data Set: Bayesian Limits on Gravitational Waves from Individual Supermassive Black Hole Binaries
• Self consistent model for the evolution of eccentric massive black hole binaries in stellar environments: implications for gravitational wave observations
• Mapping gravitational-wave backgrounds using methods from CMB analysis: Application to pulsar timing arrays
• Probing Anisotropies of the Stochastic Gravitational Wave Background with LISA
• The MeerKAT Pulsar Timing Array: The first search for gravitational waves with the MeerKAT radio telescope
• Binary super-massive black hole environments diminish the gravitational-wave signal in the pulsar timing band
• Constraining the Solution to the Last Parsec Problem with Pulsar Timing
• The second data release from the European Pulsar Timing Array V. Search for continuous gravitational wave signals
• Forecasting pulsar timing array sensitivity to anisotropy in the stochastic gravitational wave background
• The Maximal Amount of Gravitational Waves in the Curvaton Scenario
• Imprints of Supermassive Black Hole Evolution on the Spectral and Spatial Anisotropy of Nano-Hertz Stochastic Gravitational-Wave Background
• Source anisotropies and pulsar timing arrays
• The MeerKAT Pulsar Timing Array: Maps of the gravitational-wave sky with the 4.5 year data release
• How to Detect an Astrophysical Nanohertz Gravitational-Wave Background
• Spatial and Spectral Characterization of the Gravitational-wave Background with the PTA Optimal Statistic
• Measuring kinematic anisotropies with pulsar timing arrays
• Testing strengths, limitations and biases of current Pulsar Timing Arrays detection analyses on realistic data
• Resolving the nano-Hz gravitational wave sky: the detectability of eccentric binaries with PTA experiments
• The impact of large-scale galaxy clustering on the variance of the Hellings-Downs correlation: theoretical framework
• Separating deterministic and stochastic gravitational wave signals in realistic pulsar timing array datasets
• Measuring anisotropies in the PTA band with cross-correlations