Estimation of neutron star mass and radius of FRB 20240114A by identification of crustal oscillations

Hajime Sotani; Zorawar Wadiasingh; Cecilia Chirenti

doi:10.3847/2041-8213/ae5896

paper

Estimation of neutron star mass and radius of FRB 20240114A by identification of crustal oscillations

arXiv:2602.14353 · doi:10.3847/2041-8213/ae5896

Abstract

By identifying quasi-periodic oscillations (QPOs) reported in FRB 20240114A (from the Five-hundred-meter Aperture Spherical Telescope) with neutron star crustal torsional oscillations, together with experimental constraints on the incompressibility $K_{0}$ of symmetric nuclear matter at saturation density, we constrain the mass and radius of an extragalactic neutron star at redshift $z \approx 0.13$ . Identifying the low-order QPO frequencies as fundamental oscillations, and frequencies of $567.7 Hz$ or $655.5 Hz$ (rest frame) as first overtone candidates, implies neutron star mass ranges of $1.00$ -- $1.55 M_{⊙}$ or $1.17$ -- $1.76 M_{⊙}$ , respectively. The radius is also constrained, with a self-consistent value around $13$ ~km, consistent with the calculation of the NS structure within the low-mass/low-central density regime. Simultaneously, we also constrain another nuclear saturation parameter, namely the density dependence of the nuclear symmetry energy at saturation density (i.e., the slope parameter), $L$ , and determine it to be $L = 59.5 - 96.8$ MeV with $\sim 10%$ systematic uncertainty, which is broadly consistent with previous constraints on $L$ obtained from experiments and astronomical observations. Thus, a mapping of FRB QPOs to crustal torsional modes seems reasonable. This interpretation will be tested with the discovery of additional QPOs in upcoming FRB surveys.

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