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

TL;DR

This study constrains the mass, radius, and nuclear parameters of a neutron star associated with FRB 20240114A by identifying its QPOs as crustal oscillations, providing insights into neutron star structure and nuclear matter.

Contribution

It introduces a novel method linking FRB QPOs to neutron star crustal modes to estimate stellar and nuclear parameters.

Findings

Neutron star mass estimated between 1.00 and 1.76 solar masses.

Radius constrained around 13 km, consistent with low-mass neutron star models.

Nuclear symmetry energy slope parameter L constrained to 59.5-96.8 MeV.

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 $z\approx0.13$. Identifying the low-order QPO frequencies as fundamental oscillations, and frequencies of $567.7\,\mathrm{Hz}$ or $655.5\,\mathrm{Hz}$ (rest frame) as first overtone candidates, implies neutron star mass ranges of $1.00$--$1.55\,M_\odot$ or $1.17$--$1.76\,M_\odot$, 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.