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 $\approx {10}^{-8}$. 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 [Dergachev and Papa, Phys. Rev. Lett. 123, 101101 (2019)] 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 $3\times {10}^{-13}\mathrm{Hz}/\mathrm{s}$ easily accommodating sources with ellipticities of ${10}^{-7}$ at a distance of a few hundred parsecs. New outliers are found, many of which we are unable to associate with any instrumental cause.

• Received 29 April 2021
• Accepted 28 June 2021

DOI:https://doi.org/10.1103/PhysRevD.104.043003

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Open access publication funded by the Max Planck Society.

Published by the American Physical Society