A Comparison of Measured Crab and Vela Glitch Healing Parameters with Predictions of Neutron Star Models

There are currently two well-accepted models that explain how pulsars exhibitglitches, sudden changes in their regular rotational spin-down. According tothe starquake model, the glitch healing parameter, Q, which is measurable insome cases from pulsar timing, should be equal to the ratio of the moment ofinertia of the superfluid core of a neutron star (NS) to its total moment ofinertia. Measured values of the healing parameter from pulsar glitches cantherefore be used in combination with realistic NS structure models as one testof the feasibility of the starquake model as a glitch mechanism. We haveconstructed NS models using seven representative equations of state ofsuperdense matter to test whether starquakes can account for glitches observedin the Crab and Vela pulsars, for which the most extensive and accurate glitchdata are available. We also present a compilation of all measured values of Qfor Crab and Vela glitches to date which have been separately published in theliterature. We have computed the fractional core moment of inertia for stellarmodels covering a range of NS masses and find that for stable NSs in therealistic mass range 1.4 +/- 0.2 solar masses, the fraction is greater than0.55 in all cases. This range is not consistent with the observationalrestriction Q < 0.2 for Vela if starquakes are the cause of its glitches. Thisconfirms results of previous studies of the Vela pulsar which have suggestedthat starquakes are not a feasible mechanism for Vela glitches. The much largervalues of Q observed for Crab glitches (Q > 0.7) are consistent with thestarquake model predictions and support previous conclusions that starquakescan be the cause of Crab glitches.Comment: 8 pages, including 3 figures and 1 table. Accepted for publication in Ap