Constraint on the mass and radius of GRB 200415A using the high-frequency QPOs

Torsional oscillations excited in the neutron star crust strongly depend on the crust elasticity. Once one would identify the observed frequencies of a neutron star with crustal torsional oscillations, one might extract the crust or neutron star properties. In practice, it has been suggested that the crust equation of state (or nuclear saturation parameters) could be constrained by identifying the quasi-periodic oscillations (QPOs) observed in the afterglow of the magnetar giant flares with crustal torsional oscillations. On the other hand, recently high-frequency QPOs are discovered in the gamma-ray burst, GRB 200415A. Unlike the previous magnetar QPOs, only high-frequency QPOs could be observed in GRB 200415A because of the short duration of observation. Nevertheless, we can identify this observation in the same framework as in the previous magnetar QPOs by systematically examining the crustal torsional oscillations, through which we can constrain the nuclear saturation parameters. Furthermore, by consistently considering the neutron star mass and radius expected from the resultant nuclear saturation parameters, we can also constrain the neutron star mass and radius, which are more or less consistent with the other constraints from the astronomical observations.