A sensitivity curve approach to tuning a pulsar timing array in the detection era

TL;DR

This paper introduces a sensitivity curve approach to optimize pulsar timing array strategies for detecting gravitational waves, emphasizing the importance of observational tuning to enhance sensitivity to single sources and the stochastic background.

Contribution

It presents generic methods using sensitivity curves for studying PTA observational strategies and demonstrates how to optimize detection of single sources and backgrounds.

Findings

High cadence on best pulsars improves single source detection at high frequencies.

Sky-targeted campaigns offer minimal sensitivity gains.

Pulsar-term noise significantly impacts PTA sensitivity.

Abstract

As pulsar timing arrays (PTAs) transition into the detection era of the stochastic gravitational wave background (GWB), it is important for PTA collaborations to review and possibly revise their observing campaigns. The detection of a ''single source'' would be a boon for gravitational astrophysics, as such a source would emit gravitational waves for millions of years in the PTA frequency band. Here we present generic methods for studying the effects of various observational strategies, taking advantage of detector sensitivity curves, i.e., noise-averaged, frequency-domain detection statistics. The statistical basis for these methods is presented along with myriad examples of how to tune a detector towards single, deterministic signals or a stochastic background. We demonstrate that trading observations of the worst pulsars for high cadence campaigns on the best pulsars increases sensitivity to single sources at high frequencies while hedging losses in GWB and single source sensitivity at low frequencies. We also find that sky-targeted observing campaigns yield minimal sensitivity improvements compared with other PTA tuning options. Lastly, we show the importance of the uncorrelated half of the GWB, i.e. the pulsar-term, as an increasingly prominent sources of noise and show the impact of this emerging noise source on various PTA configurations.