Consistency of the Parkes Pulsar Timing Array Signal with a Nanohertz Gravitational-wave Background

Abstract

Pulsar timing array experiments have recently reported strong evidence for a common-spectrum stochastic process with a strain spectral index consistent with that expected of a nanohertz-frequency gravitational-wave background, but with negligible yet non-zero evidence for spatial correlations required for a definitive detection. However, it was pointed out by the Parkes Pulsar Timing Array (PPTA) collaboration that the same models used in recent analyses resulted in strong evidence for a common-spectrum process in simulations where none is present. In this work, we introduce a methodology to distinguish pulsar power spectra with the same amplitude from noise power spectra of similar but distinct amplitudes. The former is the signature of a spatially uncorrelated pulsar term of a nanohertz gravitational-wave background, whereas the latter could represent ensemble pulsar noise properties. We test the methodology on simulated data sets. We find that the reported common process in PPTA pulsars is indeed consistent with the spectral feature of a pulsar term. We recommend this methodology as one of the validity tests that the real astrophysical and cosmological backgrounds should pass, as well as for inferences about the spatially uncorrelated component of the background.

Splitting the lentils: Clues to galaxy/black hole coevolution from the discovery of offset relations for non-dusty versus dusty (wet-merger-built) lenticular galaxies in theMbh–M*,spheroid andMbh–M*,galaxy diagrams

“…This, in turn, benefits our expectations for the local influence of these waves on the arrival time of pulsed emission from pulsars located in an array around us (Foster & Backer 1990;Sesana et al 2008a;Burke-Spolaor et al 2019). Ongoing experiments to indirectly detect these waves include the Parkes Pulsar Timing Array (PPTA: Manchester et al 2013;Shannon et al 2013;Goncharov et al 2022), the European Pulsar Timing Array (EPTA: Lentati et al 2015;Chen et al 2021), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav: Arzoumanian et al 2021;Middleton et al 2021), plus newcomers such as the Indian Pulsar Timing Array (Tarafdar et al 2022), and the South African MeerTime Pulsar Timing Array (Spiewak et al 2022). It is thus a large global enterprise.…”

Evaluating the prevalence of spurious correlations in pulsar timing array datasets

“…There have been recent and ongoing efforts to characterise the CRN more robustly and efficiently (e.g. Goncharov et al 2022;Taylor et al 2022;Johnson et al 2022;Hazboun et al 2020). These works are crucial as PTA collaborations move toward obtaining the first positive detections of the nanohertz GWB.…”

“…While further investigations of these underlying Bayes factor distributions may be a topic of interest for future work, we suggest that improvements in the underlying inference procedure (e.g. Goncharov et al 2022) is a more appropriate route toward robust CRN inference in future.…”

“…There have been recent efforts to improve inference methods for the CRN (e.g. Goncharov et al 2022). As we will show in this work, developments such as these are necessary to consolidate recent detections of a CRN as milestones toward the detection of the GWB via spatial correlations.…”

Pulsar Timing Response to Gravitational Waves with Spherical Wave Fronts from a Massive Compact Source in the Quadrupole Approximation

“…The method of using radio pulse timing to search for gravitational waves (GWs) can be dated back to Estabrook & Wahlquist (1975), Sazhin (1978), Detweiler (1979), and Hellings & Downs (1983). A possible deviation from the expected noise has been reported by the NANOGrav team (Arzoumanian et al 2020;Antoniadis et al 2022) and has been argued by several teams (Alam et al 2021a(Alam et al , 2021bArzoumanian et al 2021aArzoumanian et al , 2021bPol et al 2021;Goncharov et al 2022;Kaiser et al 2022). It is expected that the first detection by the International Pulsar Timing Array consortium may come soon (Castelvecchi 2022).…”