The Crab glitches: incidence and cumulative effect

The fourteen glitches observed during 33 years do not show the simple pattern expected from a relaxation oscillator. They may however be regarded as three major events separated by about 12 years, the third being a group of smaller glitches. There is a step increase in slowdown rate at each glitch, whose cumulative effect makes a significant contribution to the second differential nu-ddot. The braking index "n" has previously been evaluated only between glitches: the effect of the glitches is to reduce "n" from 2.51 to 2.45. This extra effect due to the glitches would be explained by an increase in dipole field at the fractional rate of 1.5x10^-5 per annum.