On constraining the speed of gravitational waves following GW150914

TL;DR

This paper uses the GW150914 event to set model-independent bounds on the speed of gravitational waves, constraining it to be between approximately 1 and 1.7 times the speed of light, combining multiple observational bounds.

Contribution

It provides the first model-independent double-sided constraint on gravitational wave speed using LIGO data and cosmic ray observations.

Findings

Gravitational wave speed is constrained to be between 1 and 1.7 times the speed of light.

The analysis combines LIGO timing with cosmic ray bounds for a model-independent result.

Comparison with pulsar and cosmological constraints highlights the robustness of the bounds.

Abstract

We point out that the observed time delay between the detection of the signal at the Hanford and Livingston LIGO sites from the gravitational wave event GW150914 places an upper bound on the speed of propagation of gravitational waves, $c_{gw}\lesssim 1.7$ in the units of speed of light. Combined with the lower bound from the absence of gravitational Cherenkov losses by cosmic rays that rules out most of subluminal velocities, this gives a model-independent double-sided constraint $1\lesssim c_{gw}\lesssim 1.7$. We compare this result to model-specific constraints from pulsar timing and cosmology.