Title：Recent results from Pulsar Timing Arrays

Speaker：Siyuan Chen (PKU)

Special Time：3:00 pm Sep. 20th (Wednesday)

Tencent Meeting：429-1540-0486 password: 6360

Location: Lecture Hall, 3rd floor

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 North American Nanohertz Observatory for Gravitational waves (NANOGrav), Australian Parkes PTA, European and Indian PTA and Chinese PTA. They coordinate their work together in the International PTA. We hope to deepen collaboration more Chinese and South African PTA colleagues.

I will focus on the recent results that the EPTA+InPTA and CPTA collaborations have published simultaneously, each using their own independent data sets and analysis tools. Concurrently, NANOGrav and PPTA also report consistent results of a common signal with a nominal amplitude of around 2-3e-15. 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.

CV：

Siyuan Chen received his PhD in Physics and Astronomy from the University of Birmingham in the UK under the supervision of Prof. Alberto Sesana in 2018. He has been awarded the AE Hills studentship to cover the tuition fees. From 2018 to 2021, he has worked as a postdoctoral researcher at the Centre national de la recherche scientifique (CNRS) in Orleans, France, in the Laboratory for space and evironmental physics and chemistry (LPC2E). During his studies and reasearch, Siyuan Chen has been strongly involved  strongly with the European Pulsar Timing Array (EPTA), where he serves as the co-coordinator of the data analysis and astrophysics working group. Recently, he has taken a position on the Executive Committee of the EPTA. Other collaborations include the Large European Array for Pulsars (LEAP), North American Nanohertz Observatory for Gravitational waves (NANOGrav) and International Pulsar Timing Array (IPTA). At the end of 2021, he has joined the Kavli Institute for Astronomy and Astrophysics at Peking University as a postdoctoral fellow.

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