45 years of rotation of the Crab pulsar

A 45-year study of the Crab pulsar's rotation, led by Jodrell Bank Observatory since 1984, reveals a slowdown rate decrease of about 0.5 Hz from 1968, punctuated by 24 glitches—sudden spin-up events. Notably, 15 glitches occurred within an 11-year span, with each glitch partially reversing the slowdown through a step and exponential decay (320-day time constant). The cumulative effect of glitches reduces the slowdown rate decrease by ~6%. The study measures a low mean braking index of 2.342(1) over the entire period but identifies an underlying power-law slowdown with a braking index of 2.5 when glitch effects are removed. This suggests a dipolar magnetic field with an increasing inclination angle between the dipole and rotation axes, possibly influenced by additional factors like particle wind or supernova debris.

Lyne, A. G., Jordan, C. A., Graham-Smith, F., Espinoza, C. M., Stappers, B. W., & Weltevrede, P. (2014). 45 years of rotation of the Crab pulsar. Monthly Notices of the Royal Astronomical Society, 446(1), 857–864. https://doi.org/10.1093/mnras/stu2118