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Sub-torque-balance Upper Limits on Continuous Gravitational Waves from Scorpius X-1
A. G. Abac et al 2026 The Astrophysical Journal Letters 1010 .
Caption: Figure 7.
The marginalized upper limits from Figure 5, converted to limits on the ellipticity ﹩\epsilon =\frac{\left|{I}_{xx}-{I}_{yy}\right|}{{I}_{zz}}﹩ (K. Riles 2023; K. Wette 2023) of the NS in Sco X-1 (left axis scale), or alternatively, the r-mode amplitude α (right axis scale). The ellipticity assumes a moment of inertia of 1038 kg m2 and a distance of 2.8 kpc. For GW frequencies between 75 and 200 Hz, the constraints are between 3 × 10−5 and 3 × 10−6. At the highest frequencies, these are entering the range of possible ellipticities for ordinary NS matter. The r-mode amplitudes use equation (24) of B. J. Owen (2010); the best limits of ∼5 × 10−4 are probably still slightly above what one might expect in Sco X-1 (B. J. Owen & B. Rajbhandari (2025) and references therein).
© 2026. The Author(s). Published by the American Astronomical Society.