Search for continuous gravitational waves from small-ellipticity sources at low frequencies
Vladimir Dergachev, M. A. Papa
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 $\ensuremath{\approx}{10}^{\ensuremath{-}8}$. 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 $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}\text{ }\text{ }\mathrm{Hz}/\mathrm{s}$ easily accommodating sources with ellipticities of ${10}^{\ensuremath{-}7}$ at a distance of a few hundred parsecs. New outliers are found, many of which we are unable to associate with any instrumental cause.