Minimum Glitch of the Crab Pulsar and the Crustquake as a Trigger Mechanism

We discuss the minimum glitch size of Crab observed by Espinoza et al. (2014). Modelling the crustquake as a trigger mechanism we estimate the size of the broken plate. The plate size obtained, D $\sim 100 m$ is comparable to plate size estimates for PSR J1119--6127. The plate size naturally leads to an estimate of the number of unpinned vortices involved in the glitch, $N \sim 10^{13} $. This number is of the same order in all Crab and Vela pulsar glitches. The mimimum glitch relates the constancy of all these numbers among different pulsars to the basic plate size involved in crust breaking. This in turn depends on the critical strain angle $\theta_{cr}$ of the Coulomb lattice in the neutron star crust. The minimum glitch size implies $\theta_{cr} \sim 10^{-1}$ in agreement with theoretical and computational estimates.