Constraints on r-modes and mountains on millisecond neutron stars in binary systems

TL;DR

This paper reports an advanced all-sky search for continuous gravitational waves from neutron stars in binary systems within 300-500 Hz, setting new sensitivity limits and excluding certain neutron star configurations.

Contribution

It presents the first binary system search in this frequency range using Advanced-LIGO data, achieving over an order of magnitude increased sensitivity.

Findings

No signals detected in the searched parameter space.

Excluded neutron star deformations greater than 3e-6 within 1 kpc.

Constrained r-mode emission levels to alpha ~ few 1e-4 within 1 kpc.

Abstract

Continuous gravitational waves are nearly monochromatic signals emitted by asymmetries in rotating neutron stars. These signals have not yet been detected. Deep all-sky searches for continuous gravitational waves from isolated neutron stars require significant computational expense. Deep searches for neutron stars in binary systems are even more expensive, but potentially these targets are more promising emitters, especially in the hundreds-Hz region, where ground-based gravitational wave detectors are most sensitive. We present here an all-sky search for continuous signals with frequency between 300 and 500 Hz, from neutron stars in binary systems with orbital period between 15 and 60 days, and projected semi-major axis between 10 and 40 light-seconds. This is the only binary search on Advanced-LIGO data that probes this frequency range. Compared to previous results, our search is over an order of magnitude more sensitive. We do not detect any signals, but our results exclude plausible and unexplored neutron star configurations, for example, neutron stars with relative deformations greater than 3e-6 within 1 kpc from Earth and r-mode emission at the level of alpha ~ few 1e-4 within the same distance.