Observational constraints on neutron star crust-core coupling during glitches

Abstract

We demonstrate that observations of glitches in the Vela pulsar can be used to investigate the strength of the crust-core coupling in a neutron star, and suggest that recovery from the glitch is dominated by torque exerted by the re-coupling of superfluid components of the core that were decoupled from the crust during the glitch. Assuming that the recoupling is mediated by mutual friction between the superfluid neutrons and the charged components of the core, we use the observed magnitudes and timescales of the shortest timescale components of the recoveries from two recent glitches in the Vela pulsar to infer the fraction of the core that is coupled to the crust during the glitch, and hence spun up by the glitch event. Within the framework of a two-fluid hydrodynamic model of glitches, we analyze whether crustal neutrons alone are sufficient to drive the glitch activity observed in the Vela pulsar. We use two sets of neutron star equations of state (EOSs), both of which span crust and core consistently and cover a range of the slope of the symmetry energy at saturation density $30<L<120$ MeV. One set produces maximum masses $\approx$2.0$M_{\odot }$, the second $\approx$2.6$M_{\odot }$. We also include the effects of entrainment of crustal neutrons by the superfluid lattice. We find that for medium to stiff EOSs, observations imply $>70\%$ of the moment of inertia of the core is coupled to the crust during the glitch, though for softer EOSs $L\approx 30$MeV as little as $5\%$ could be coupled. No EOS is able to reproduce the observed glitch activity with crust neutrons alone, but extending the region where superfluid vortices are strongly pinned into the core by densities as little as 0.016fm${}^{-3}$ above the crust-core transition density restores agreement with the observed glitch activity.

12 pages, 7 figures, 2 tables; submitted to MNRAS

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• New Gogny interaction suitable for astrophysical applications
• Giant Pulsar Glitches and the Inertia of Neutron-Star Crusts
• Constraints on pulsar masses from the maximum observed glitch
• Postglitch exponential relaxation of radio pulsars and magnetars in terms of vortex creep across flux tubes
• Nuclear fourth-order symmetry energy and its effects on neutron star properties in the relativistic Hartree-Fock theory
• Study of the core-crust transition in neutron stars with finite-range interactions: the dynamical method
• A superfluid perspective on neutron star dynamics
• Core and crust contributions in pulsar glitches: constraints from the slow rise of the largest glitch observed in the Crab pulsar
• Discovery of a Glitch in the Accretion Powered Pulsar SXP 1062
• Modelling pulsar glitches: the hydrodynamics of superfluid vortex avalanches in neutron stars
• A universal formula for the relativistic correction to the mutual friction coupling time-scale in neutron stars
• Prior probability distributions of neutron star crust models
• Core and crust contributions in overshooting glitches: the Vela pulsar 2016 glitch
• Effects of general relativity on glitch amplitudes and pulsar mass upper bounds
• The effect of non-linear mutual friction on pulsar glitch sizes and rise times
• Turbulent, pinned superfluids in neutron stars and pulsar glitch recoveries
• Hydrodynamic simulations of pulsar glitch recovery
• Revisiting the post-glitch relaxation of the 2000 Vela glitch with the neutron star equation of states in the Brueckner and relativistic Brueckner theories
• Probing neutron star interiors with pulsar glitches
• Vortex Avalanches and Collective Motion in Neutron Stars
• Inner crust of neutron stars with mass-fitted Skyrme interaction
• Imprints of high-density nuclear symmetry energy on the crustal fraction of neutron star moment of inertia
• The Jodrell Bank Glitch Catalogue: 106 new rotational glitches in 70 pulsars
• Measuring the crust-superfluid coupling time-scale for 105 UTMOST pulsars with a Kalman filter