The micro-glitch in PSR B1821-24 : A case for a strange pulsar?

The single glitch observed in PSR B1821-24, a millisecond pulsar in M28, is unusual on two counts. First, the magnitude of this glitch is at least an order of magnitude smaller ($\mathrm{\Delta }\nu \mathrm{/}\nu \sim {10}^{-11}$) than the smallest glitch observed to date. Secondly, all other glitching pulsars have strong magnetic fields with $B\text{gsim}{10}^{11}G$ and are young, whereas PSR B1821-24 is an old recycled pulsar with a field strength of $2.25\times {10}^{9}G$. We have suggested earlier that some of the recycled pulsars could actually be strange quark stars. In this work we argue that the crustal properties of such a {\em strange} pulsar are just right to give rise to a glitch of this magnitude, explaining the scarcity of larger glitches in millisecond pulsars.