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. A non-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 gamma repeaters arise from the fundamental torsional oscillations and that the mass 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.