Reading signatures of supermassive binary black holes in pulsar timing array observations

Abstract

We find the inferred properties of the putative gravitational wave background in the second data release of the European Pulsar Timing Array to be in better agreement with theoretical expectations under the improved noise model. In particular, our improved noise models show consistency of the background's strain spectral index with the value of -2/3, favoring the population of supermassive black hole binaries as the origin of the background. Our results further suggest that the observed gravitational wave emission is the dominant source of the binary energy loss, with no evidence of environmental effects or eccentric orbits. At the reference gravitational wave frequency of yr${}^{-1}$, we also find a lower power-law strain amplitude of the background than in previous data analyses. This mitigates some of the tensions of the strain amplitude with the expected number density and mass scale of binaries discussed in the literature. However, we show that it is mostly affected by strong covariance of the amplitude and the strain spectral index at yr${}^{-1}$, whereas the strain amplitude at 0.1 yr${}^{-1}$ and the strain amplitude at yr${}^{-1}$ assuming a fixed spectral index of -2/3 remains unaffected. Our results highlight the importance of accurate noise models for correctly inferring properties of the gravitational wave background.

9 pages, 4 figures

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Cited by in corpus (3)

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• Accurate pulsar timing array residual variances and correlation of the stochastic gravitational wave background
• The NANOGrav 15 yr Data Set: Customized Chromatic Noise Models