Pulsar-timing measurement of the circular polarization of the stochastic gravitational-wave background

Pulsar-timing arrays (PTAs) are in the near future expected to detect a stochastic gravitational-wave background (SGWB) produced by a population of inspiralling supermassive black hole binaries. In this work, we consider a background that can be anisotropic and circularly polarized. We use the expansion of the intensity and the circular polarization in terms of spherical harmonics and the overlap reduction functions for each term in this expansion. We propose an unbiased real-space estimator that can separate the intensity and circular-polarization contributions of the SGWB to pulsar-timing-residual correlations and then validate the estimator on simulated data. We compute the signal-to-noise ratio of a circularpolarization component that has a dipole pattern under different assumptions about the PTA. We find that a nearly maximal circular-polarization dipole may be detectable, which can aid in determining whether or not the background is dominated by a handful of bright sources.

Automated summary

This work investigates the detection of a stochastic gravitational-wave background (SGWB) produced by inspiralling supermassive black hole binaries using pulsar-timing arrays (PTAs). An unbiased real-space estimator is proposed to separate the intensity and circular-polarization contributions of the SGWB to pulsar-timing-residual correlations, and is validated on simulated data. The study finds that a nearly maximal circular-polarization dipole may be detectable, aiding in determining whether or not the background is dominated by a handful of bright sources.