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 (28)

• Array Programming with NumPy
• 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
• Searching for the nano-Hertz stochastic gravitational wave background with the Chinese Pulsar Timing Array Data Release I
• 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
• The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars
• Expected properties of the first gravitational wave signal detected with pulsar timing arrays
• 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
• Mapping gravitational-wave backgrounds using methods from CMB analysis: Application to pulsar timing arrays
• 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
• 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
• Gravitational wave radiometry: Mapping a stochastic gravitational wave background
• Variance of the Hellings-Downs Correlation
• Hellings and Downs correlation of an arbitrary set of pulsars
• 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
• The MeerKAT Pulsar Timing Array: The $4.5$-year data release and the noise and stochastic signals of the millisecond pulsar population
• Evaluating the prevalence of spurious correlations in pulsar timing array datasets
• Detecting a Stochastic Gravitational-Wave Background: The Overlap Reduction Function
• Mapping the Gravitational-wave Sky with LISA: A Bayesian Spherical Harmonic Approach
• Consistency of the Parkes Pulsar Timing Array Signal with a Nanohertz Gravitational-wave Background
• Exploring Proxies for the Supermassive Black Hole Mass Function: Implications for Pulsar Timing Arrays
• Improving pulsar timing precision through superior Time-of-Arrival creation

Cited by in corpus (7)

• The MeerKAT Pulsar Timing Array: The first search for gravitational waves with the MeerKAT radio telescope
• Sub-GeV dark matter and nano-Hertz gravitational waves from a classically conformal dark sector
• Measuring anisotropies in the PTA band with cross-correlations
• Mitigating cosmic variance in the Hellings-Downs curve: a Cosmic Microwave Background analogy
• Dissecting the nanoHz 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