WoU-MMA: Pulsar Timing Arrays Around the World CHIME in on Gravitational Waves

Gravitational wave (GW) astronomy is rapidly expanding our ability to study the extreme universe, opening new “windows on the universe. Like electromagnetic radiation, gravitational radiation has a spectrum of possible frequencies, spanning many orders of magnitude. A project at the University of Montana (UM) focuses on the low frequency end of the spectrum – nanohertz gravitational waves observed by pulsar timing arrays (PTAs). In 2023, PTAs around the world reported evidence for a detection of a low-frequency stochastic GW background, most likely arising from the cosmic merger history of supermassive black hole binaries. This project will improve the pulsar timing models for PTAs, add new observatories to the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) dataset, and create combined International Pulsar Timing Array (IPTA) datasets. This principal investigator (PI) will sponsor annual field trips to observatories participating in multi-messenger astrophysics (MMA) for members of the University of Montana Society of Physics Students (SPS). The principal investigator will also support physics students in beginning their research career and will leverage the existing UM planetarium to create a public outreach show about MMA. Pulsar timing arrays search for GWs by observing large sets of millisecond pulsars over decades with radio telescopes and generating high-precision timing models for each pulsar. The residuals from fitting these timing models to observations show characteristic signals indicative of the presence of the gravitational wave background. Therefore, to improve the GW detector, PTAs must improve their pulsar timing models, which is the primary goal of the project. This will enable the characterization of the GW background and possibly of GW from individual supermassive black hole binary sources while also providing a rich dataset for studies of neutron stars. This work will pursue two primary directions: first, the PI will lead efforts to add new observatories to the NANOGrav dataset. In the near future, this will entail adding data from CHIME/Pulsar and in the further future, this will include data from the proposed DSA-2000 experiment. Second, this work will focus on the creating combined IPTA datasets. This work will support the PI in leading the third such dataset and will allow the development of an improved time-of-arrival generation procedure for the fourth IPTA dataset. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.