Host: Zhen Pan

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Abstract:

Pulsar Timing Arrays (PTAs) are entering a new era of nano-Hertz gravitational wave (GW) astronomy with evidence for a GW signal found in several PTA data sets, CPTA, EPTA, InPTA, NANOGrav, PPTA and MPTA. They are working together in the IPTA to combine the data sets and analyze the truely best upcoming global PTA data set, IPTA DR3, to be able to conclusively confirm the detection of nano-Hertz GWs. In addition, the GammaPTA project is also advancing and offers a complementary observing frequency range to radio PTAs. In my presentation I will review the status of current global PTA efforts and focus on the challenges that PTAs are faced in the near future.

One challenge is the robust and efficient analysis of the increasingly larger data sets and more and more complex models needed. The combination of all the data sets from all the regional PTAs into an IPTA DR3 will involve more than 100 pulsars, 20 years of observations and ~10 telescopes. The analysis and robust modelling of the noise properties may require new methods to be developped. These need to address the computational speed of our calculations as well as providing robust noise models, which can affect the properties of significance of a possible GW signal. I will provide an overview of the examples of the effects of noise modelling and ongoing efforts to make our analysis quicker and more reliable.

Another challenge is to identify and characterize the origin of the tentative GW signal in the PTA data sets. Two classes of sources are often discussed in the literature, one being super massive black hole binaries (SMBHBs) and the other more exotic sources, mostly related to cosmology. SMBHBs are formed when two galaxies merge. Several processes will drive the evolution of the binary orbit. Measurements of a GW background can help to address the question on how SMBHBs evolve over a cosmic time scale. Possible cosmological sources include cosmic strings, ultra light dark matter and phase transitions in the Early era of the Universe. I will attempt to review the current status of astrophysical and new physics interpretation efforts from the PTA community and how we will move forward into the post-detection era.

Biography:

Siyuan Chen has received his PhD in 2018 in Physics and Astronomy from the University of Birmingham in the UK. After which he has worked as a postdoctoral researcher at the LPC2E, CNRS Orleans in France 2018 to 2021 and at the Kavli Institute for Astronomy and Astrophysics at Peking Universtity 2021 to 2024. In April 2024, Dr Siyuan Chen joined the Shanghai Astronomical Observatory, Chinese Academy of Sciences as an associate researcher. He has worked on the astrophysical interpretation and the analysis of Pulsar Timing Array data sets. He is a member of several PTA collaborations, the EPTA, CPTA, NANOGrav and the IPTA, which have received several awards, the ICBS Frontiers of Science Award, RAS Group Achievement Award and AAS HEAD Bruno Rossi award.