Title：The Parkes Pulsar Timing Array – project overview and searches for nanohertz-frequency gravitational waves

Speaker：Andrew Zic，Australia Telescope National Facility

Special Time：10:00 am July 12th (Friday)

Tencent Meeting：337-830-570 password: 6360

Location: Lecture Hall, 3rd floor

Abstract：

The Parkes Pulsar Timing Array (PPTA) is a major project on Murriyang, CSIRO’s Parkes Radio Telescope, with the primary aim of detecting nanohertz-frequency gravitational waves. In this talk, I will present an overview of the project up until our third data release, which incorporates high-precision pulsar timing observations spanning 18 years. I will describe our search for an isotropic stochastic gravitational-wave background (GWB) in the PPTA-DR3. We recover a common-spectrum noise process among the pulsars, which exhibits a characteristic amplitude of A = 2.0±0.2×10^-15 for a strain spectrum h = A (f / f _1yr )^(-2/3). In a hierarchical Bayesian search for inter-pulsar correlations, we recover a signal consistent with the Hellings-Downs correlations expected from an isotropic GWB with a false alarm probability of p ≲ 0.014. However, contrary to expectations for an isotropic GWB, we demonstrate that the signal strength is apparently time-dependent. I will discuss these results in the context of historical and contemporary analyses, and conclude with an overview of ongoing work in the collaboration.

CV：Dr. Andrew Zic is an “Impossible Without You” Research Scientist at the Australia Telescope National Facility in CSIRO. His research interests lie in gravitational-wave and time-domain radio astronomy, spanning gravitational-wave searches with precision pulsar timing to studies of powerful radio bursts from Galactic radio transients. Andrew completed his PhD in 2020 at The University of Sydney, studying “Cool Stellar Activity at Low Radio Frequencies”. Following this, he began work as a postdoc jointly at Macquarie University and CSIRO, working on the Parkes Pulsar Timing Array project. In 2023, he transitioned to his current position as Research Scientist at CSIRO, and will commence as a CSIRO Bolton Research Scientist later in 2024. For his work co-leading the PPTA DR3, Andrew was awarded the 2024 Astronomical Society of Australia Louise Webster Prize for outstanding research by a scientist early in their post-doctoral career. In July 2024, Andrew will accept a Frontiers of Science Award from the International Congress for Basic Science on behalf of the PPTA collaboration, for their role in the coordinated international announcements of the first evidence for nanohertz-frequency gravitational waves. Aside from his research, Andrew enjoys cooking and sampling delicious food from around the world and playing music with his band.