Magnetar giant flare oscillations and the nuclear symmetry energy

Abstract

*If the observed quasi-periodic oscillations in magnetar flares are partially confined to the crust, then the oscillation frequencies are unique probes of the nuclear physics of the neutron star crust. We study crustal oscillations in magnetars including corrections for a finite Alfvén velocity. Our crust model uses a new nuclear mass formula that predicts nuclear masses with an accuracy very close to that of the Finite Range Droplet Model. This mass model for equilibrium nuclei also includes shell corrections and an updated neutron-drip line. We perturb our crust model to predict axial crust modes and assign them to observed giant flare quasiperiodic oscillation frequencies from SGR 1806-20. We find magnetar crusts that match observations for various magnetic field strengths, entrainment of the free neutron gas in the inner crust, and crust-core transition densities. We find that observations can be reconciled with smaller values of the symmetry energy slope parameter, L, if there is a significant amount of entrainment of the neutrons by the superfluid or if the crust-core transition density is large. We also find neutron star masses and radii which are in agreement with expectations from what is known about low-density matter from nuclear experiment. Matching observations with a field-free model we obtain the approximate values of M = 1.35 M and R = 11.9 km. Matching observations using a model with the surface dipole field of SGR 1806-20 (B = 2.4 × 10 15 G) we obtain the approximate values of M = 1.25 M and R = 12.4 km.

Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties

“…In Ref. [64], the fundamental shear mode was matched either with the 18 Hz QPO or the 28 Hz QPO, based on the employed EOS model. In this section, I calculate the frequency of the fundamental crustal shear mode (n = 0, l = 2) with free-slip boundary conditions based on the results for the innercrust shear properties.…”

Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations

“…Israel et al 2005;Strohmayer & Watts 2005;) have stimulated theoretical research in neutron star oscillations. QPOs have been interpreted as toroidal shear oscillations of the solid crust by various groups, and approaches to constrain the nuclear equation of state (EoS) of the crust have started (see Duncan 1998;Messios et al 2001;Strohmayer & Watts 2005;Piro 2005;Sotani et al 2007;Samuelsson & Andersson 2007;Steiner & Watts 2009;Sotani et al 2013a;Deibel et al 2014;Sotani et al 2016, and references therein). However, since the neutron stars where QPOs are observed have the strongest magnetic fields known, it was realized that the interaction of the crust with the magnetic field leads to a very effective coupling of the two (Levin 2006(Levin , 2007Glampedakis et al 2006).…”

Hyperon Puzzle: Hints from Quantum Monte Carlo Calculations

“…The measurements of the large mass values of the millisecond pulsars PSR J1903+0327 (1.67(2)M ) [17] and in particular PSR J1614-2230 (1.97(4)M ) [18] and PSR J0348+0432 (2.01(4)M ) [19] suggest a stiff EOS. Other NS observations of masses and radii seem to disfavor a very soft EOS of neutron star matter [20][21][22][23]. This seems to contradict the appearance of strange baryons in high-density matter, at least according to nonrelativistic many-body approaches.…”