The search for continuous gravitational waves from small-ellipticity sources at low frequencies

TL;DR

This paper reports an all-sky search for continuous gravitational waves from neutron stars with very small ellipticity in the low-frequency range, using an improved analysis pipeline on LIGO data, resulting in new outliers of interest.

Contribution

The study extends the sensitivity of the Falcon pipeline to lower frequencies and smaller ellipticities, enabling detection of neutron stars up to 44 parsecs away in a previously hard-to-probe region.

Findings

Detection of new outliers not linked to instrumental artifacts.

Enhanced sensitivity due to increased coherence length.

Search capability for neutron stars with ellipticity as low as 1e-8.

Abstract

We present the results of an all-sky search for continuous gravitational wave signals with frequencies in the 20-500 Hz range from neutron stars with ellipticity of 1e-8. This frequency region is particularly hard to probe because of the quadratic dependence of signal strength on frequency. The search employs the Falcon analysis pipeline on LIGO O2 public data. Compared to previous Falcon analyses the coherence length has been quadrupled, with a corresponding increase in sensitivity. This enables us to search for small ellipticity neutron stars in this low frequency region up to 44 pc away. The frequency derivative range is up to 3e-13 Hz/s easily accommodating sources with ellipticities of 1e-7 and a corresponding factor of 10 increase in reach. New outliers are found, many of which we are unable to associate with any instrumental cause.