The MeerKAT Pulsar Timing Array: Maps of the gravitational-wave sky with the 4.5 year data release

Abstract

In an accompanying publication, the MeerKAT Pulsar Timing Array (MPTA) collaboration reports tentative evidence for the presence of a stochastic gravitational-wave background, following observations of similar signals from the European and Indian Pulsar Timing Arrays, NANOGrav, the Parkes Pulsar Timing Array and the Chinese Pulsar Timing Array. If such a gravitational-wave background signal originates from a population of inspiraling supermassive black-hole binaries, the signal may be anisotropically distributed on the sky. In this Letter we evaluate the anisotropy of the MPTA signal using a spherical harmonic decomposition. We discuss complications arising from the covariance between pulsar pairs and regularisation of the Fisher matrix. Applying our method to the 4.5 yr dataset, we obtain two forms of sky maps for the three most sensitive MPTA frequency bins between 7 -21 nHz. Our "clean maps'' estimate the distribution of gravitational-wave strain power with minimal assumptions. Our radiometer maps answer the question: is there a statistically significant point source? We find a noteworthy hotspot in the 7 nHz clean map with a $p$-factor of $p=0.015$ (not including trial factors). Future observations are required to determine if this hotspot is of astrophysical origin.

References in corpus (61)

• Array Programming with NumPy
• HEALPix -- a Framework for High Resolution Discretization, and Fast Analysis of Data Distributed on the Sphere
• The NANOGrav 15-year Data Set: Evidence for a Gravitational-Wave Background
• Cosmic strings
• Search for an isotropic gravitational-wave background with the Parkes Pulsar Timing Array
• Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I
• Gravitational Wave Experiments and Early Universe Cosmology
• The second data release from the European Pulsar Timing Array III. Search for gravitational wave signals
• PSRCHIVE and PSRFITS An Open Approach to Radio Pulsar Data Storage and Analysis
• Detecting a stochastic background of gravitational radiation: Signal processing strategies and sensitivities
• Detecting gravitational waves from cosmological phase transitions with LISA: an update
• Detection methods for stochastic gravitational-wave backgrounds: a unified treatment
• The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
• Limits on the Stochastic Gravitational Wave Background from the North American Nanohertz Observatory for Gravitational Waves
• Low-frequency gravitational radiation from coalescing massive black hole binaries in hierarchical cosmologies
• Ultra-Low Frequency Gravitational Radiation from Massive Black Hole Binaries
• Expected properties of the first gravitational wave signal detected with pulsar timing arrays
• The stochastic background: scaling laws and time to detection for pulsar timing arrays
• Gravitational-wave cosmology across 29 decades in frequency
• A review of gravitational waves from cosmic domain walls
• The MeerKAT Telescope as a Pulsar Facility: System verification and early science results from MeerTime
• The Local Nanohertz Gravitational-Wave Landscape From Supermassive Black Hole Binaries
• Characterising gravitational wave stochastic background anisotropy with Pulsar Timing Arrays
• Detection of Anisotropies in the Gravitational-Wave Stochastic Background
• Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: IV. Implications for LISA
• Mapping gravitational-wave backgrounds using methods from CMB analysis: Application to pulsar timing arrays
• Searching For Anisotropic Gravitational-wave Backgrounds Using Pulsar Timing Arrays
• A study of spatial correlations in pulsar timing array data
• Probing the anisotropies of a stochastic gravitational-wave background using a network of ground-based laser interferometers
• The Final Parsec Problem
• Directional limits on persistent gravitational waves using LIGO S5 science data
• Identifying and mitigating noise sources in precision pulsar timing data sets
• Time-domain Implementation of the Optimal Cross-Correlation Statistic for Stochastic Gravitational-Wave Background Searches in Pulsar Timing Data
• A radiometer for stochastic gravitational waves
• Interactions between multiple supermassive black holes in galactic nuclei: a solution to the final parsec problem
• Collisionless loss-cone refilling: there is no final parsec problem
• The MeerKAT Pulsar Timing Array: The first search for gravitational waves with the MeerKAT radio telescope
• From Bright Binaries To Bumpy Backgrounds: Mapping Realistic Gravitational Wave Skies With Pulsar-Timing Arrays
• Gravitational wave radiometry: Mapping a stochastic gravitational wave background
• Mapping the gravitational wave background
• Galaxy Rotation and Rapid Supermassive Black Hole Binary Coalescence
• The optimal search for an astrophysical gravitational-wave background
• Variance of the Hellings-Downs Correlation
• Limits on anisotropy in the nanohertz stochastic gravitational-wave background
• Noise-marginalized optimal statistic: A robust hybrid frequentist-Bayesian statistic for the stochastic gravitational-wave background in pulsar timing arrays
• Hellings and Downs correlation of an arbitrary set of pulsars
• Frequency-Dependent Template Profiles for High Precision Pulsar Timing
• The neutron star mass, distance, and inclination from precision timing of the brilliant millisecond pulsar J0437$-$4715
• Forecasting pulsar timing array sensitivity to anisotropy in the stochastic gravitational wave background
• Probing anisotropies of gravitational-wave backgrounds with a space-based interferometer: geometric properties of antenna patterns and their angular power
• The MeerKAT Pulsar Timing Array: The $4.5$-year data release and the noise and stochastic signals of the millisecond pulsar population
• Fisher formalism for anisotropic gravitational-wave background searches with pulsar timing arrays
• Evaluating the prevalence of spurious correlations in pulsar timing array datasets
• Detecting a Stochastic Gravitational-Wave Background: The Overlap Reduction Function
• Insights into searches for anisotropies in the nanohertz gravitational-wave background
• Mapping the Gravitational-wave Sky with LISA: A Bayesian Spherical Harmonic Approach
• Searching for anisotropy in the distribution of binary black hole mergers
• Consistency of the Parkes Pulsar Timing Array Signal with a Nanohertz Gravitational-wave Background
• Model Dependence of Bayesian Gravitational-Wave Background Statistics for Pulsar Timing Arrays
• Exploring Proxies for the Supermassive Black Hole Mass Function: Implications for Pulsar Timing Arrays
• Improving pulsar timing precision through superior Time-of-Arrival creation

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• The MeerKAT Pulsar Timing Array: The first search for gravitational waves with the MeerKAT radio telescope
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• Measuring anisotropies in the PTA band with cross-correlations
• Mitigating cosmic variance in the Hellings-Downs curve: a Cosmic Microwave Background analogy
• Dissecting the nanohertz gravitational wave sky: Frequency-correlated anisotropy induced by eccentric supermassive black hole binaries
• Searching for Anisotropy in the Gravitational Wave Background Using the Parkes Pulsar Timing Array
• Finite Populations & Finite Time: The Non-Gaussianity of a Gravitational Wave Background