Effect of superfluidity on neutron star oscillations

Abstract

We consider how superfluidity of dripped neutrons in the crust of a neutron star affects the frequencies of the crust's fundamental torsional oscillations.Anon-negligible superfluid part of dripped neutrons, which do not comove with nuclei, acts to reduce the enthalpy density and thus enhance the oscillation frequencies. By assuming that the quasi-periodic oscillations observed in giant flares of soft gammarepeaters arise from the fundamental torsional oscillations and that themass and radius of the neutron star are in the range 1.4≤M/M⊙ ≤1.8 and 10≤R≤14 km, we constrain the density derivative of the symmetry energy as 100 ≲ L ≲ 130 MeV, which is far more severe than the previous one, L ≳ 50 MeV, derived by ignoring the superfluidity. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.