POSTGLITCH RELAXATION OF THE VELA PULSAR AFTER ITS 1ST 8 LARGE GLITCHES - A REEVALUATION WITH THE VORTEX CREEP MODEL

We present a comprehensive reevaluation of eight of the nine glitches observed to date from the Vela pulsar, and the postglitch relaxation f ollowing each glitch. All glitch data sets can be described in terms o f three distinct components of short and intermediate time scale expon ential relaxation, followed by a long-term recovery of the glitch-indu ced change in the spin-down rate that is linear in t, DELTAOMEGA(c)(t) is-proportional-to t. We interpret the short and the intermediate tim e scale exponential relaxation, characterized by relaxation times of 1 0 hr, 3d.2, and 32d as the linear response of vortex creep in those re gions of the pinned superfluid in the neutron star crust through which no sudden vortex motion occurred at the time of the glitch. The long- term recovery is interpreted as the nonlinear response of vortex creep regions. In addition, there are regions of the crustal superfluid whi ch cannot sustain a vortex density or vortex creep current, but which play a significant role in determining the angular momentum balance. T he tendency of glitches to leave permanent spin-up remnants is explain ed as a discrete internal torque which in glitches, couples part of th e crustal superfluid to the observed crust. We find that, on average, the theoretically expected interglitch intervals agree quite well with the observed intervals. The same set of short and intermediate relaxa tion times, with similar values of moments of inertia for the various components of the crustal superfluid, yield good fits for all postglit ch data sets. Furthermore, these relaxation times and moments of inert ia are compatible with previous theoretical estimates. A moment of ine rtia fraction of at least 0.024 is implied for the crustal superfluid. This result rules out neutron star models based on soft equations of state.