Efficacy of crustal superfluid neutrons in pulsar glitch models

Abstract

In order to assess the ability of purely crust-driven glitch models to match the observed glitch activity in the Vela pulsar, we conduct a systematic analysis of the dependence of the fractional moment of inertia of the inner crustal neutrons on the stiffness of the nuclear symmetry energy at saturation density L. We take into account both crustal entrainment and the fact that only a fraction Yg of the core neutrons may couple to the crust on the glitch-rise time-scale. We use a set of consistently generated crust and core compositions and equations of state (EoSs) which are fit to results of low-density pure neutron matter calculations. When entrainment is included at the level suggested by recent microscopic calculations and the core is fully coupled to the crust, the model is only able to account for the Vela glitch activity for a 1.4 M{N-ary circled dot operator} star if the EoS is particularly stiff L > 100 MeV. However, an uncertainty of about 10 per cent in the crust-core transition density and pressure allows for the Vela glitch activity to be marginally accounted for in the range L ≈ 30-60 MeV consistent with a range of experimental results. Alternatively, only a small amount of core neutrons need be involved. If less than 50 per cent of the core neutrons are coupled to the crust during the glitch, we can also account for the Vela glitch activity using crustal neutrons alone for EoSs consistent with the inferred range of L. We also explore the possibility of Vela being a high-mass neutron star, and of crustal entrainment being reduced or enhanced relative to its currently predicted values.