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

Sato-Polito, Gabriela; Kamionkowski, Marc

doi:10.1103/physrevd.106.023004

Cited by 23 publications

(15 citation statements)

References 40 publications

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“…Rather than imposing positivity via rejection, a more elegant approach was developed almost simultaneously for ground-based (Payne et al 2020), space-borne (Banagiri et al 2021), and PTA (Taylor et al 2020) anisotropy searches through which the square root of the GWB power was first expressed on a spherical-harmonic basis, thereby naturally imposing positive behavior on the GWB itself. Other techniques have been adapted from CMB analyses to map the polarization content of the GWB (Gair et al 2014;Kato & Soda 2016;Hotinli et al 2019;Sato-Polito & Kamionkowski 2022;Liu & Ng 2022), although these have yet to be applied to real data. Finally, techniques using data-driven bases for anisotropy modeling show promise; by computing eigenskies of the noise-weighted PTA response map, the GWB power distribution can be efficiently built from a compact number of basis terms (Cornish & van Haasteren 2014;Ali-Haïmoud et al 2020.…”

Section: Introduction § Nsf Astronomy and Astrophysics Postdoctoral F...mentioning

confidence: 99%

The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

Agazie

Anumarlapudi

Archibald

et al. 2023

ApJL

665

283

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We report multiple lines of evidence for a stochastic signal that is correlated among 67 pulsars from the 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves. The correlations follow the Hellings–Downs pattern expected for a stochastic gravitational-wave background. The presence of such a gravitational-wave background with a power-law spectrum is favored over a model with only independent pulsar noises with a Bayes factor in excess of 1014, and this same model is favored over an uncorrelated common power-law spectrum model with Bayes factors of 200–1000, depending on spectral modeling choices. We have built a statistical background distribution for the latter Bayes factors using a method that removes interpulsar correlations from our data set, finding p = 10−3 (≈3σ) for the observed Bayes factors in the null no-correlation scenario. A frequentist test statistic built directly as a weighted sum of interpulsar correlations yields p = 5 × 10−5 to 1.9 × 10−4 (≈3.5σ–4σ). Assuming a fiducial f −2/3 characteristic strain spectrum, as appropriate for an ensemble of binary supermassive black hole inspirals, the strain amplitude is 2.4 − 0.6 + 0.7 × 10 − 15 (median + 90% credible interval) at a reference frequency of 1 yr−1. The inferred gravitational-wave background amplitude and spectrum are consistent with astrophysical expectations for a signal from a population of supermassive black hole binaries, although more exotic cosmological and astrophysical sources cannot be excluded. The observation of Hellings–Downs correlations points to the gravitational-wave origin of this signal.

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Section: Introduction § Nsf Astronomy and Astrophysics Postdoctoral F...mentioning

confidence: 99%

The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

Agazie

Anumarlapudi

Archibald

et al. 2023

ApJL

665

283

View full text Add to dashboard Cite

show abstract

“…Rather than imposing positivity via rejection, a more elegant approach was developed almost simultaneously for ground-based (Payne et al 2020), space-borne (Banagiri et al 2021), and PTA (Taylor et al 2020) anisotropy searches through which the square root of the GWB power was first expressed on a spherical-harmonic basis, thereby naturally imposing positive behavior on the GWB itself. Other techniques have been adapted from CMB analyses to map the polarization content of the GWB (Gair et al 2014;Kato & Soda 2016;Belgacem & Kamionkowski 2020;Liu & Ng 2022;Sato-Polito & Kamionkowski 2022), although these have yet to be applied to real data. Finally, techniques using data-driven bases for anisotropy modeling show promise; by computing eigen-skies of the noise-weighted PTA response map, the GWB power distribution can be efficiently built from a compact number of basis terms (Cornish & van Haasteren 2014;Ali-Haïmoud et al 2020.…”

Section: Introductionmentioning

confidence: 99%

The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background

Agazie,

Anumarlapudi,

Archibald

et al. 2023

ApJL

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The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has reported evidence for the presence of an isotropic nanohertz gravitational-wave background (GWB) in its 15 yr data set. However, if the GWB is produced by a population of inspiraling supermassive black hole binary (SMBHB) systems, then the background is predicted to be anisotropic, depending on the distribution of these systems in the local Universe and the statistical properties of the SMBHB population. In this work, we search for anisotropy in the GWB using multiple methods and bases to describe the distribution of the GWB power on the sky. We do not find significant evidence of anisotropy. By modeling the angular power distribution as a sum over spherical harmonics (where the coefficients are not bound to always generate positive power everywhere), we find that the Bayesian 95% upper limit on the level of dipole anisotropy is (C l=1/C l=0) < 27%. This is similar to the upper limit derived under the constraint of positive power everywhere, indicating that the dipole may be close to the data-informed regime. By contrast, the constraints on anisotropy at higher spherical-harmonic multipoles are strongly prior dominated. We also derive conservative estimates on the anisotropy expected from a random distribution of SMBHB systems using astrophysical simulations conditioned on the isotropic GWB inferred in the 15 yr data set and show that this data set has sufficient sensitivity to probe a large fraction of the predicted level of anisotropy. We end by highlighting the opportunities and challenges in searching for anisotropy in pulsar timing array data.

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“…This is smaller in size than the expected anisotropies of the astrophysical SGWB in the PTA band (see e.g. [28][29][30][31][32] and in particular [33] for a recent study). But, as for the CMB, it is potentially well larger than intrinsic cosmological anisotropies (see, e.g., the studies [34][35][36][37][38][39][40]).…”

Section: Introductionmentioning

confidence: 70%

Kinematic anisotropies and pulsar timing arrays

Tasinato

2023

Phys. Rev. D

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Doppler anisotropies, induced by our relative motion with respect to the source rest frame, are a guaranteed property of stochastic gravitational wave backgrounds of cosmological origin. If detected by future pulsar timing array measurements, they will provide interesting information on the physics sourcing gravitational waves, which is hard or even impossible to extract from measurements of the isotropic part of the background only. We analytically determine the pulsar response function to kinematic anisotropies, including possible effects due to parity violation, to features in the frequency dependence of the isotropic part of the spectrum, as well as to the presence of extra scalar and vector polarizations. For the first time, we show how the sensitivity to different effects crucially depends on the pulsar configuration with respect to the relative motion among frames. Correspondingly, we propose examples of strategies of detection, each aimed at exploiting future measurements of kinematic anisotropies for characterizing distinct features of the cosmological gravitational wave background.

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

Cited by 23 publications

References 40 publications

The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

The NANOGrav 15 yr Data Set: Evidence for a Gravitational-wave Background

The NANOGrav 15 yr Data Set: Search for Anisotropy in the Gravitational-wave Background

Kinematic anisotropies and pulsar timing arrays

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