The Targeted Standard Siren Cosmology with Pulsar Timing Arrays

TL;DR

This paper proposes a targeted search method for gravitational wave sources with Pulsar Timing Arrays, enabling precise cosmological measurements like the Hubble constant despite large sky localizations.

Contribution

It introduces a targeted search approach for SMBHBs with PTAs, improving the potential for using these sources as standard sirens in cosmology.

Findings

CPTA can measure the Hubble constant with 2 km/s/Mpc precision.

Targeted searches are robust against host galaxy confusion.

Method enhances the use of PTA-detected SMBHBs for cosmology.

Abstract

The sky localisation of about $10$ to $100~\text{deg}^2$, which is expected to be achieved in all-sky blind searches for gravitational waves from supermassive black hole binaries (SMBHBs) with Pulsar Timing Array (PTA) experiments, has long been posed as a prohibitive factor in utilising these sources as standard sirens for precision cosmology. We propose a solution to this problem, which makes use of targeted searches rather than all-sky blind searches for SMBHBs. Using our simulated data informed by current PTA observations, we show that the Chinese Pulsar Timing Array (CPTA) alone could infer the Hubble constant with a precision of 2~km/s/Mpc. Such precision in an independent cosmological probe could provide decisive support in the resolution of the Hubble tension. We demonstrate the application of our method to several simultaneously observed SMBHBs, as well as the method's robustness against confusion between the host galaxies of SMBHB sources in realistic observing scenarios.