The SKAO Pulsar Timing Array

TL;DR

The paper argues that SKAO will revolutionize nanohertz gravitational-wave astronomy by enabling a large, highly precise pulsar timing array. It outlines the full spectrum of detectable signals, from a stochastic GWB and continuous SMBHBs to early-Universe and exotic phenomena, and describes how SKAO’s sensitivity, frequency coverage, and sub-array capabilities will enhance detection and sky-mapping through improved pulsar sampling, VLBI-distance measurements, and multi-wavelength synergy. It provides realistic forecasts for GWB and individual-source sensitivities, discusses noise mitigation strategies (including ISM propagation and solar wind modeling), and details observational requirements and cross-facility collaborations. The overall result is a concrete, multi-faceted roadmap showing that SKAO PTA will map the nanohertz GW sky, constrain SMBHB populations and cosmological sources, and enable precision tests of gravity and fundamental physics in the 2030s and beyond.

Abstract

Pulsar timing arrays (PTAs) are ensembles of millisecond pulsars observed for years to decades. The primary goal of PTAs is to study gravitational-wave astronomy at nanohertz frequencies, with secondary goals of undertaking other fundamental tests of physics and astronomy. Recently, compelling evidence has emerged in established PTA experiments for the presence of a gravitational-wave background. To accelerate a confident detection of such a signal and then study gravitational-wave emitting sources, it is necessary to observe a larger number of millisecond pulsars to greater timing precision. The SKAO telescopes, which will be a factor of three to four greater in sensitivity compared to any other southern hemisphere facility, are poised to make such an impact. In this chapter, we motivate an SKAO pulsar timing array (SKAO PTA) experiment. We discuss the classes of gravitational waves present in PTA observations and how an SKAO PTA can detect and study them. We then describe the sources that can produce these signals. We discuss the astrophysical noise sources that must be mitigated to undertake the most sensitive searches. We then describe a realistic PTA experiment implemented with the SKA and place it in context alongside other PTA experiments likely ongoing in the 2030s. We describe the techniques necessary to search for gravitational waves in the SKAO PTA and motivate how very long baseline interferometry can improve the sensitivity of an SKAO PTA. The SKAO PTA will provide a view of the Universe complementary to those of the other large facilities of the 2030s.

Figures (8)

• Figure 1: Inter-pulsar correlations from recent pulsar timing array gravitational-wave searches. We show the correlations derived from the the European Pulsar Timing Array and Indian Pulsar Timing Array 2023AA...678A..50E, the North American Nanohertz Observatory for Gravitational Waves 2023ApJ...951L...8A, the MeerKAT Pulsar Timing Array 2025MNRAS.536.1489M, the Parkes Pulsar Timing Array 2023ApJ...951L...6R, and the Chinese Pulsar Timing Array 2023RAA....23g5024X.
• Figure 2: A comparison of PTA sensitivities. Curves were obtained using methodology discussed in 2022PASA...39...27S.
• Figure 3: Strain sensitivity curves for the MeerKAT Pulsar Timing Array and a conceptual SKAO Pulsar Timing Array after observing for $5$, $10$, and $15$ years. The left panel shows the sensitivity to a GWB. The dashed line shows the spectrum of a GWB at an amplitude of $A_{\rm yr}=2\times 10^{-15}$. The right panel shows the sky-averaged sensitivity to single source. The black points highlight individual sources detectable by the PTA. The curves highlight where pulsar timing array experiments have the greatest sensitivity.
• Figure 4: Predicted number of detectable single sources with SKAO-PTA. The open dots represent the median number of resolved continuous gravitational waves resolved from the 200 SMBHB populations, while error bars represent the 64 and 32 percentiles of the distribution.
• Figure 5: Sky distribution of the SKAO PTA pulsars (light-blue) and the SMBHBs detected as continuous gravitational waves (dark violet) in a single realization SMBHB population. The size of the dark violet points is weighted by the CGW $\rm S/N$