Alternative neural-network follow-up for all-sky FrequencyHough in continuous gravitational-wave searches
Continuous gravitational waves are long-lived signals emitted by spinning neutron stars (NSs) or boson clouds around black holes. While the Milky Way is expected to host $\mathrm{O}(10^{8}-10^{9})$ NSs, only $\mathrm{O}(10^{3})$ are currently identified through electromagnetic observations. This large observational gap motivates searches based on alternative messengers. In particular, all-sky searches for continuous gravitational waves (GWs) offer a unique opportunity to detect NSs that are electromagnetically silent or otherwise undiscovered. By exploring a broad region of parameter space without any a priori source information, these searches can probe the vast hidden NS population of our Galaxy. In this work, we present a novel way to include a Neural Network (NN) classifier into an all-sky search strategy for isolated NSs. Starting from candidates produced by the FrequencyHough pipeline running on data from ground-based detectors such as LIGO and Virgo, the proposed method improves sensitivity without increasing computational cost and can be parallelized across multiple detectors to enhance detection probability and reduce false alarms. We analyze data from the third observing run (O3) --- April 1, 2019 to March 27, 2020 --- and focus on the frequency range [129, 229] Hz and spin-down interval [$-2.5\cdot10^{-9}, 1.0\cdot10^{-9}$] Hz/s. The model is trained on noise constructed to be statistically consistent with real O3 data and tested on real O3 data. Results show robust performance in distinguishing signal from noise, even at low strain, and successful identification of hardware injections outside the training spin-down range.