Relativistic correction to the r-mode frequency in light of multi-messenger constraints

TL;DR

This paper examines how relativistic effects and multi-messenger constraints influence the r-mode oscillation frequencies in neutron stars, refining search parameters for gravitational wave detection and constraining nuclear equations of state.

Contribution

It provides updated estimates of r-mode frequencies incorporating recent multi-messenger constraints and derives universal relations with tidal deformability for neutron stars.

Findings

R-mode frequency range is slightly higher than previous estimates.

Narrow band frequency can increase by 8-25% depending on compactness.

Universal relations link r-mode frequency with tidal deformability.

Abstract

R-mode oscillations of rotating neutron stars are promising candidates for continuous gravitational wave (GW) observations. The r-mode frequencies for slowly rotating Newtonian stars are well-known and independent of the equation of state (EOS) but for neutron stars, several mechanisms can alter the r-mode frequency of which the relativistic correction is dominant and relevant for most of the neutron stars. The most sensitive searches for continuous GWs are those for known pulsars for which GW frequencies are in targeted narrow frequency bands of few Hz. In this study, we investigate the effect of several state-of-the-art multi-messenger constraints on the r-mode frequency for relativistic, slowly rotating, barotropic stars. Imposing these recent constraints on the EOS, we find that the r-mode frequency range is slightly higher from the previous study and the narrow band frequency range can increase upto 8-25% for the most promising candidate PSR J0537-6910 depending on the range of compactness. We also derive universal relations between r-mode frequency and dimensionless tidal deformability which can be used to estimate the dynamical tide of the r-mode resonant excitation during the inspiral signal. These results can be used to construct the parameter space for r-mode searches in gravitational wave data and also constrain the nuclear equation of state following a successful r-mode detection.