Search for continuous gravitational waves from neutron stars in five globular clusters in the first part of the fourth LIGO-Virgo-KAGRA observing run

TL;DR

This study conducted sensitive directed searches for continuous gravitational waves from unknown neutron stars in five globular clusters using LIGO data, but found no signals, setting new upper limits on gravitational wave amplitudes.

Contribution

First application of the WEAVE semi-coherent method to search for continuous waves in globular clusters with LIGO data, achieving the most sensitive upper limits to date.

Findings

No gravitational wave signals detected.

Achieved median 95% upper limits as low as ~4.2 x 10^-26.

Most sensitive results across explored parameter space.

Abstract

We present the results of directed searches for continuous gravitational waves from unknown neutron stars in five Milky Way globular clusters. We carry out the searches in the LIGO data from the first eight months of the fourth LIGO-Virgo-KAGRA observing run using the WEAVE semi-coherent program, which sums matched-filter detection-statistic values over many time segments spanning the observation period. No gravitational wave signal is detected in the search band of 20-475 Hz for assumed source ages greater than 300 years. Injections of simulated continuous wave signals in the data indicate that we achieve the most sensitive results to date across most of the explored parameter space volume, obtaining median 95% confidence level upper limits as low as $\sim 4.2 \times 10^{-26}$ near 282 Hz for NGC 6397.