Constraints on the velocity of gravitational waves from NANOGrav 15-year data set

TL;DR

This paper uses 15 years of pulsar timing data to place a lower bound on the speed of gravitational waves in the nanohertz frequency range, supporting their propagation at or near the speed of light.

Contribution

It introduces a novel method using overlap reduction function deviations in pulsar timing arrays to constrain gravitational wave velocity at low frequencies.

Findings

Lower bound on gravitational wave velocity: v > 0.87c

Supports the prediction that gravitational waves travel at light speed

Extends velocity constraints to nanohertz frequency range

Abstract

General relativity predicts that gravitational waves propagate at the speed of light. Although ground-based gravitational-wave detectors have successfully constrained the velocity of gravitational waves in the high-frequency range, extending this constraint to the lower frequency range remains a challenge. In this work, we utilize the deviations in the overlap reduction function for a gravitational-wave background within pulsar timing arrays to investigate the velocity of gravitational waves in the nanohertz frequency band. By analyzing the NANOGrav 15-year data set, we obtain a well-constrained lower bound for the velocity of gravitational waves that $v \gtrsim 0.87\,c$, where $c$ is the speed of light.