Efficacy of crustal superfluid neutrons in pulsar glitch models

Within the framework of recent hydrodynamic models of pulsar glitches, we explore systematically the dependence on the stiffness of the nuclear symmetry energy at sat-uration density L, of the fractional moment of inertia of the pinned neutron superfluid in the crust G and the initial post-glitch relative acceleration of the crust K, both of which are confronted with observational constraints from the Vela pulsar. We allow for a variable fraction of core superfluid neutrons coupled to the crust on glitch rise timescales, Yg. We assess whether the crustal superfluid neutrons are still a tenable angular momentum source to explain the Vela glitches when crustal entrainment is included. The observed values G and K are found to provide nearly orthogonal con-straints on the slope of the symmetry energy, and thus taken together offer potentially tight constraints on the equation of state. However, when entrainment is included at the level suggested by recent microscopic calculations, the model is unable to reproduce the observational constraints on G and K simultaneously, and is limited to L> 100 MeV and Yg ≈ 0 when G is considered alone. One solution is to allow the pinned superfluid vortices to penetrate the outer crust, which leads to a constraint of L. 45 MeV and Yg. 0.04 when G and K are required to match observations simultaneously. When one allows the pinned vortices to penetrate into the crust by densities of up to 0.082 fm−3 above crust-core transition density (a total density of 0.176 fm−3) for L = 30 MeV, and 0.048 fm−3 above crust-core transition density (a total density of 0.126 fm−3) for L = 60 MeV, the constraint on G is satisfied for any value of Yg. We discuss the implications of these results for crust-initiated glitch models