2018MNRAS.479.4735S -
Mon. Not. R. Astron. Soc., 479, 4735-4748 (2018/October-0)
Constraints on the nuclear equation of state and the neutron star structure from crustal torsional oscillations.
SOTANI H., IIDA K. and OYAMATSU K.
Abstract (from CDS):
We systematically examine torsional shear oscillations of neutron star crusts by newly taking into account the possible presence of the phase of cylindrical nuclei. In this study, we neglect an effect of magnetic fields, under which the shear oscillations can be damped by the magnetic interaction. First, by identifying the low-frequency quasi-periodic oscillations (QPOs) observed in the soft-gamma repeaters (SGRs) as the fundamental torsional oscillations, we constrain the slope parameter of the nuclear symmetry energy, L, for reasonable values of the star's mass M and radius R. Meanwhile, we find that the 1st overtone of torsional oscillations obtained for given M and R can be expressed well as a function of a new parameter σ≡(K_04L5)1/9^, where K0 is the incompressibility of symmetric nuclear matter. Assuming that the lowest of the QPO frequencies above 500 Hz observed in SGR 1806-20 comes from the 1st overtone, we can constrain the value of s. Then, for each neutron star model, such a value of L, as can be obtained from the observed low-frequency QPOs, translates to the optimal value of K0 via the above constraint on s. Finally, its consistency with allowed values of K0 from empirical giant monopole resonances leads to neutron star models with relatively low mass and large radius, which are qualitatively similar to the prediction in earlier investigations. This result suggests that L ≃ 58-73 MeV, even when uncertainties in the neutron superfluid density inside the phase of cylindrical nuclei are allowed for.
Abstract Copyright:
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
Journal keyword(s):
equation of state - stars: neutron - stars: oscillations
Simbad objects:
3
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