Applying the "snowplow" model for pulsar glitches to constrain nuclear symmetry energy

Abstract

Glitches in pulsars are occasional, sudden increases in their rotation frequency as the pulsar otherwise steadily spins down. A broad class of glitch models suppose the sudden spin-ups are due to angular momentum transfer between some of the crustal superfluid neutrons and the rigid crust plus anything that couples to it on timescales shorter than the superfluid-crust coupling time. Using a set of neutron star equations of state (EOS) which span the experimentally constrained range of asymmetric nuclear matter properties, and estimates of the strength of the coupling between the crust and the core superfluid neutrons, we calculate the moment of inertia (MoI) of crustal superfluid neutrons involved in storing angular momentum in the glitch process. Following the recent, microscopically based "snowplow" model for glitches, we restrict the calculation to just those superfluid neutron vortices that are strongly pinned to the crustal lattice, a region which corresponds to an equatorial annulus of the inner crust. We compare calculations to observational estimates of the average rate of angular momentum transfer between superfluid neutrons and the rest of the star in the Vela pulsar, and also the relative acceleration of the crust post-glitch estimated from the 2002 Vela glitch. We found that to match the observations of the glitch sizes and recovery from Vela glitches, a value of L 50 MeV for the density slope of the symmetry energy at saturation density is required and the coupling between core superfluid neutrons and crust is relatively weak.