The $m=1$ instability \& gravitational wave signal in binary neutron star mergers

TL;DR

This paper investigates the development and detectability of the $m=1$ gravitational wave mode in binary neutron star merger remnants, highlighting its potential for revealing neutron star equation of state details and its observability with current detectors.

Contribution

It demonstrates that the $m=1$ instability develops rapidly and can be as strong or stronger than the $m=2$ mode, and assesses its detectability with Earth-based gravitational wave detectors.

Findings

The $m=1$ mode develops quickly and can be as strong as the $m=2$ mode.

The $m=1$ mode occurs at roughly half the frequency of the $m=2$ mode.

Detection prospects extend to about 14 Mpc for direct detection and 100 Mpc for triggered searches.

Abstract

We examine the development and detectability of the $m=1$ instability in the remnant of binary neutron star mergers. The detection of the gravitational mode associated with the $m=1$ degree of freedom could potentially reveal details of the equation of state. We analyze the post-merger epoch of simulations of both equal and non-equal mass neutron star mergers using three realistic, microphysical equations of state and neutrino cooling. Our studies show such an instability develops generically and within a short dynamical time to strengths that are comparable or stronger than the $m=2$ mode which is the strongest during the early post-merger stage. We estimate the signal to noise ratio that might be obtained for the $m=1$ mode and discuss the prospects for observing this signal with available Earth-based detectors. Because the $m=1$ occurs at roughly half the frequency of the more powerful $m=2$ signal and because it can potentially be long-lived, targeted searches could be devised to observe it. We estimate that with constant amplitude direct detection of the mode could occur up to a distance of roughly $14\,\mathrm{Mpc}$ whereas a search triggered by the inspiral signal could extend this distance to roughly $100\,\mathrm{Mpc}$.