The effect of superfluid hydrodynamics on pulsar glitch sizes and waiting times

Pulsar glitches, sudden jumps in frequency observed in many radio pulsars, may be the macroscopic manifestation of superfluid vortex avalanches on the microscopic scale. Small-scale quantum mechanical simulations of vortex motion in a decelerating container have shown that such events are possible and predict power-law distributions for the size of the events, and exponential distributions for the waiting time. Despite a paucity of data, this prediction is consistent with the size and waiting time distributions of most glitching pulsars. Nevertheless, a few object appear to glitch quasi-periodically, and exhibit many large glitches, while a recent study of the Crab pulsar has suggested deviations from a power-law distribution for smaller glitches. In this Letter, we incorporate the results of quantum mechanical simulations in a macroscopic superfluid hydrodynamics simulation. We show that the effect of vortex coupling to the neutron and proton fluids in the star naturally leads to deviations from power-law distributions for sizes, and from exponential distributions for waiting times, and we predict a cutoff in the size distribution for small glitches.