Title: Recent Results from Pulsar Timing Arrays

Speaker: Dr. Siyuan Chen (Kavli Institute for Astronomy and Astrophysics, Peking University)

Time: 14:00pm, January 19, 2024

Location: 3-302, PMO Xianlin Campus

Abstract: Pulsar Timing Arrays (PTAs) search for nHz gravitational waves by timing the radio signals from a network of stable millisecond pulsars and looking for a spatially correlated common signal in the data set. We expect to find a gravitational wave background (GWB) first, followed by possible individual sources. PTAs have reported the finding of evidence for such a GWB signal in various data sets, namely NANOGrav, Australian PPTA, EPTA+InPTA and CPTA. They coordinate their work together in the IPTA. We hope to deepen collaboration with more Chinese and South African PTA colleagues.

I will focus on the recent results that the CPTA and EPTA+InPTA collaborations have published simultaneously, each using their own independent data sets and analysis tools. In the same coordinated process, NANOGrav and PPTA also report consistent results of a common signal with a nominal amplitude of around 2-3e-15 at the same time. Measurements of the characteristic spatial correlations required for a GWB vary between the different PTAs. However, a general positive trend can be noticed with some evidence ~2 to 4.5 sigmas in favour of the gravitational wave origin of the common signal. This putative signal can be tested against both cosmological and astrophysical sources for a GWB and be used to put constraints for various theories. Efforts are ongoing to combine these new data sets to form the basis for the next IPTA DR3 combination in the coming year. The IPTA DR3 should provide the best sensitivity for searching and characterising the common signal yet.