All-sky search for continuous gravitational-wave signals from unknown neutron stars in binary systems in the first part of the fourth LIGO-Virgo-KAGRA observing run

TL;DR

This study carries out a blind all-sky search for continuous gravitational waves from unknown neutron stars in binary systems using the first part of LIGO-Virgo-KAGRA O4a data, targeting 100–350 Hz with orbital periods 7–15 days and a_p = 5–15 light-seconds. Employing the GPU-accelerated fasttracks pipeline with a novel parameter-space box partitioning, the authors implement a two-step detection strategy (Hough-like persistence followed by track-aware power) and perform a follow-up with longer coherence-time MCMC analyses via PyFstat, including a stringent known-lines veto. No credible astrophysical CW signals were detected; injection campaigns yield a 95% detectable strain depth of h0^95% ≈ (1.62 ± 0.3) × 10^−25 near 200 Hz, representing a ~1.5× improvement over O3a results and enabling constraints on nearby neutron-star ellipticities (ε ≲ 10^−5 for sources within a few kpc). The work demonstrates the efficacy of fasttracks and box-based partitioning for large-scale CW searches and informs expectations for future detector networks and targeted CW population studies.

Abstract

We present the results of a blind all-sky search for continuous gravitational-wave signals from neutron stars in binary systems using data from the first part of the fourth observing run (O4a) using LIGO detectors data. Rapidly rotating, non-axisymmetric neutron stars are expected to emit continuous gravitational waves, whose detection would significantly improve our understanding of the galactic neutron star population and matter under extreme conditions, while also providing valuable tests of general relativity. Neutron stars in binary systems likely constitute a substantial fraction of the unobserved galactic population and, due to potential mass accretion, may emit stronger gravitational-wave signals than their isolated counterparts. This search targets signals from neutron stars with frequencies in the 100-350 Hz range, with orbital periods between 7 and 15 days and projected semi-major axes between 5 and 15 light-seconds. The analysis employs the GPU-accelerated fasttracks pipeline. No credible astrophysical signals were identified, and, in the absence of a detection, we report search sensitivity estimates on the population of neutron stars in binary systems in the Milky Way.

Figures (18)

• Figure 1: Comparison of the O3a and O4a multi IFO power spectral density using the data from the H1 and L1 LIGO detectors. The grey area indicates the search frequency range.
• Figure 2: Binary parameter space covered in the search. Large black dots indicate known pulsars with possible CW emission frequencies in the search range, while grey points correspond to sources outside this range. The boxed rectangular region denotes the portion of the binary parameter space explored in this search. Source: ATNF Pulsar Catalogue Manchester:2004bp.
• Figure 3: Total number of boxes per 0.125 Hz frequency band across the full search range. The lettered regions (A-E) correspond to the frequency intervals defined in Table \ref{['table:frequency_regions']}. The dashed horizontal line marks the minimum enforced number of boxes ($10^4$). Sudden changes in the number of boxes correspond to transitions between regions where either the minimum box constraint or the $10^8$ templates-per-box criterion dominates the partitioning as explained in App. \ref{['sec:partitioning']}.
• Figure 4: Highest CR values per frequency band. Arrows indicate frequency bands where the highest value is above 20.
• Figure 5: Number of candidates per $0.125$ Hz band with CR above the threshold, as a function of frequency. Frequency regions A through E correspond to those defined in Table \ref{['table:frequency_regions']}. Each black dot represents the number of candidates above threshold in a single band. Red dots indicate bands that were fully or partially vetoed due to contamination from known instrumental artifacts listed in the O4a lines list Goetz:T2400204.