On the fast recovery of the Vela pulsar from its christmas 1988 glitch

Abstract

THE Vela pulsar, whose most recent (eighth) glitch occurred during an observing session1, is the first to have been 'caught in the act'. Post-glitch timing observations2 of the rapid (≲ 1 day) recovery of the pulsar's rotation put significant constraints on the conventional model of a glitch, according to which vortices in the rotating superfluid interior of the neutron star, whose ends are pinned to nuclei in the star's crust, abruptly move to new pinned locations3. The large initial jump in the spin-down rate Ω and its prompt recovery seem to imply that an improbably large 20% of the total moment of inertia resides in the crust. We show here, however, that the fast response can be understood in terms of the dynamics of a portion of the pinned crustal superfluid4,5, amounting to ∼5.4 × 10-3 of the total moment of inertia, linearly coupled to the star's superfluid interior. This fraction is consistent with values previously deduced for the Vela pulsar6 and others, including PSR0355+54 (ref. 4), which also showed a large jump7 in Ω̇. By modelling the post-glitch relaxation, we estimate the vortex pinning energy at ∼0.3 MeV, also consistent with earlier estimates.