Neutron star mass–radius constraints using the high-frequency quasi-periodic oscillations of GRB 200415A

¹ Theoretical Astrophysics, IAAT, University of Tübingen, 72076 Tübingen, Germany
e-mail: sotani@yukawa.kyoto-u.ac.jp
² Astrophysical Big Bang Laboratory, RIKEN, Saitama 351-0198, Japan
³ Interdisciplinary Theoretical & Mathematical Science Program (iTHEMS), RIKEN, Saitama 351-0198, Japan
⁴ Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece

Received: 9 March 2023
Accepted: 19 June 2023

Abstract

Context. Quasi-periodic oscillations (QPOs) observed in a giant flare of a strongly magnetized neutron star (magnetar) carry crucial information for extracting the properties od neutron stars.

Aims. The aim of this study is to constrain the mass and radius of the neutron star model for GRB 200415A by identifying the observed QPOs with crustal torsional oscillations and comparing these with experimental constraints on the nuclear matter properties.

The frequencies of the crustal torsional oscillations are determined by solving the eigenvalue problem with the Cowling approximation, assuming a magnetic field of about 10¹⁵ G.

Methods. We find that the observed QPOs can be identified with several overtones of crustal oscillations for carefully selected combinations of the nuclear saturation parameters. Thus, we can inversely constrain the neutron star mass and radius for GRB 200415A by comparing them to the values of nuclear saturation parameters obtained from terrestrial experiments.

Results. We impose further constraints on the neutron star mass and radius while the candidate neutron star models examined here are consistent with the constraints obtained from other available astronomical and experimental observations.