Constraints on Neutron Star Crusts From Oscillations in Giant Flares

TL;DR

This paper investigates how observations of neutron star oscillations during giant flares can constrain the nuclear physics of the crust, especially the symmetry energy's density dependence, with implications for identifying seismic modes.

Contribution

It demonstrates the sensitivity of crustal shear mode frequencies to the nuclear symmetry energy and proposes using oscillation data to constrain nuclear physics parameters.

Findings

Fundamental shear mode frequency depends on the nuclear symmetry energy.

Different oscillation frequencies can indicate whether crustal or core modes are observed.

Future observations can distinguish between models based on oscillation frequencies.

Abstract

We show that the fundamental seismic shear mode, observed as a quasi-periodic oscillation in giant flares emitted by highly-magnetized neutron stars, is particularly sensitive to the nuclear physics of the crust. The identification of an oscillation at ~ 30 Hz as the fundamental crustal shear mode requires a nuclear symmetry energy that depends very weakly on density near saturation. If the nuclear symmetry energy varies more strongly with density, then lower frequency oscillations, previously identified as torsional Alfven modes of the fluid core, could instead be associated with the crust. If this is the case, then future observations of giant flares should detect oscillations at around 18 Hz. An accurate measurement of the neutron skin thickness of lead will also constrain the frequencies predicted by the model.