Wide parameter-space O3 search for continuous gravitational waves from unknown neutron stars in binary systems

TL;DR

This paper reports on a novel search for continuous gravitational waves from unknown neutron stars in binary systems, covering higher frequencies and shorter orbital periods than previous efforts, setting new constraints on neutron star properties.

Contribution

First search to explore gravitational-wave frequencies above 520 Hz and orbital periods below 3 days in binary neutron star systems using advanced detectors.

Findings

No signals detected in the searched parameter space.

Set the most stringent constraints to date on neutron star ellipticities and r-mode amplitudes.

Excluded neutron stars within 100 pc rotating faster than 495 Hz with ellipticities above 5.2e-8.

Abstract

Continuous gravitational waves, i.e., persistent and nearly-monochromatic signals emitted by asymmetric spinning neutron stars, remain elusive. Searches for these signals from unknown binary systems are the most computationally challenging, but they are essential, given that binary accretion provides a natural mechanism for creating the required asymmetry, and around half of the known pulsars rotating above 25 Hz are part of a binary system. Here we report on a search of a large uncharted parameter-space region: for the first time we cover gravitational-wave frequencies above 520 Hz (from 50 to 1000 Hz), and, for the first time with advanced detectors, orbital periods lower than 3 days are explored. No signal is detected, and we set the most stringent constraints to date on the amplitude of signals of this kind. Our results exclude with $95\%$ confidence neutron stars within 100 pc and rotating faster than $\sim$ 495 Hz from having ellipticities above $5.2 \times 10^{-8}$. Within the same distance our results also exclude r-mode amplitudes above $1.5 \times 10^{-6}$ for stars rotating faster than $\sim$ 740 Hz.