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 Y g of the core neutrons may couple to the crust on the glitch-rise timescale. We use a set of consistently-generated crust and core compositions and equations-of-state which are fit to results of lowdensity 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 1.4M star if the equation of state is particularly stiff L > 100 MeV. However, an uncertainty of about 10% in the crust-core transition density and pressure allows for the Vela glitch activity to be marginally accounted for in the range L ≈ 30 − 60MeV consistent with a range of experimental results. Alternatively, only a small amount of core neutrons need be involved. If less than 50% 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.

Gravitational waves from isolated neutron stars: Mass dependence of r -mode instability

“…The only reasonable constraint on mass of Vela pulsar is that it should exceed about one solar mass according to core-collapse supernova simulations. Therefore, the present calculations suggest that without entrainment, the crust is enough to explain the Vela glitch data and with entrainment, the crust is not enough since the mass of Vela pulsar would be below one solar mass ( Fig.-5), in accordance with other studies [70][71][72][73][74].…”

Long-term statistics of pulsar glitches triggered by a Brownian stress accumulation process

“…The other factor is I c . There are two popular scenarios for this quantity, as discussed in Section 3 of Melatos et al (2015): (a) if the crust is a thin crystalline lattice and the rest of the star is composed of a superfluid we have I c /I 0 ∼ 10 −2 , where I 0 is the total moment of inertia of the star (Andersson et al 2012;Hooker et al 2015); (b) if the crust has most of the interior superfluid pinned and co-rotating with it (via magnetic flux tubes or charged particles), with only a bit of the inner crust superfluid decoupled, we have I c /I 0 ∼ 1 (Link et al 1999;Lyne et al 2000;Espinoza et al 2011). We do not explore which of these scenarios is more likely, as both have strong support in the literature.…”

Persistent Gravitational Radiation From Glitching Pulsars

“…Recent work by Chamel (2012) adds weight to the latter scenario by showing that the effective neutron mass characterizing nondissipative entrainment is significantly larger than the bare neutron mass, implying decreased superfluid mobility relative to the crustal lattice. Hence the angular momentum reservoir is larger than the inner crust superfluid can provide, according to most nuclear theories (Andersson et al 2012;Hooker et al 2015). A key unknown facing both scenarios is how strongly neutron vortices pin to magnetic fluxoids in the core.…”