Sub-torque-balance Upper Limits on Continuous Gravitational Waves from Scorpius X-1

Authors

• A. G. Abac, Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)
• I. Abouelfettouh, LIGO Hanford
• Teviet Creighton, The University of Texas Rio Grande ValleyFollow
• Mario C. Diaz, The University of Texas Rio Grande ValleyFollow
• Raul Alberto Espinosa Perez, The University of Texas Rio Grande Valley
• J. Lawrence, The University of Texas Rio Grande Valley
• Francisco Llamas Villarreal, The University of Texas Rio Grande Valley
• Miriam Ramos Arevalo, The University of Texas Rio Grande Valley
• Soma Mukherjee, The University of Texas Rio Grande ValleyFollow
• Gaukhar Nurbek, The University of Texas Rio Grande ValleyFollow
• Volker Quetschke, The University of Texas Rio Grande ValleyFollow
• Wenhui Wang, The University of Texas Rio Grande Valley

Document Type

Article

Publication Date

10-20-2026

Abstract

We present the results of a search for continuous gravitational waves (GWs) from the low-mass X-ray binary Scorpius X-1 using LIGO data from the first part of the fourth LIGO–Virgo–KAGRA observing run. By applying the resampling version of the cross-correlation pipeline to search for signal frequencies f0 between 25 and 200 Hz (corresponding to neutron star spin frequencies of 12.5–100 Hz for GWs due to triaxiality, or ∼15–20 to ∼120–150 Hz for GWs due to r-modes), we are able to achieve longer coherence times than before, and for the first time set upper limits below the standard torque balance level, independent of neutron star spin inclination, for 50 Hz ≲ f0 ≲ 200 Hz. The most sensitive upper limits on the gravitational wave amplitude h0, at the upper end of the frequency band searched, approach 5 × 10−26 marginalized over inclination angle and 2 × 10−26 assuming the most favorable inclination. The marginalized upper limits correspond to a sensitivity depth of 70–75 Hz−1/2, improving sensitivity considerably over previous searches. Expressed as constraints on the triaxial deformation of the neutron star, the limits correspond to an ellipticity of 3 × 10−5 if the GW frequency f0 is 75 Hz and 3 × 10−6 if f0 = 200 Hz, approaching deformations that could be supported by ordinary nuclear matter. Outliers from the search were ruled out as potential signals by a combination of hierarchical follow-up and analysis of additional data from later in the observing run.

Comments

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Recommended Citation

Abac, A. G., I. Abouelfettouh, F. Acernese, K. Ackley, A. Adam, C. Adamcewicz, S. Adhicary et al. "Sub-Torque-Balance upper limits on continuous gravitational waves from Scorpius X-1." The Astrophysical Journal Letters 1010, no. 2 (2026): L23. https://doi.org/10.3847/2041-8213/aea296

Publication Title

The Astrophysical Journal Letters

DOI

10.3847/2041-8213/aea296