Astrometry meets Pulsar Timing Arrays: Synergies for Gravitational Wave Detection

TL;DR

This paper investigates how combining high-precision astrometry with pulsar timing arrays can enhance the detection and characterization of low-frequency gravitational waves, especially in identifying their origins.

Contribution

It derives analytical expressions for astrometric responses to gravitational waves, introduces optimal estimators, and demonstrates improved constraints through joint data analysis.

Findings

Cross-correlation of astrometry and PTA data improves SGWB constraints.

Derived covariant expressions for astrometric response to SGWB.

Forecasted enhanced sensitivity to SGWB parameters.

Abstract

High-precision astrometry offers a promising approach to detect low-frequency gravitational waves, complementing pulsar timing array (PTA) observations. We explore the response of astrometric measurements to a stochastic gravitational wave background (SGWB) in synergy with PTA data. Analytical, covariant expressions for this response are derived, accounting for the presence of a possible dipolar anisotropy in the SGWB. We identify the optimal estimator for extracting SGWB information from astrometric observations and examine how sensitivity to SGWB properties varies with the sky positions of stars and pulsars. Using representative examples of current PTA capabilities and near-future astrometric sensitivity, we demonstrate that cross-correlating astrometric and PTA data can improve constraints on SGWB properties, compared to PTA data alone. The improvement is quantified through Fisher forecasts for the SGWB amplitude, spectral tilt, and dipolar anisotropy amplitude. In the future, such joint constraints could play a crucial role in identifying the origin of SGWB signals detected by PTAs.