A glitch in the Crab Pulsar

Until last year the pulsar in the Crab Nebula, PSR 0531 + 21, had suffered two major glitches, or jumps in rotation rate, since it was discovered in 1968. The first, in 1969, involved a fractional change in period of ΔP/P ≅10-8 while the second, in 1975, was much larger with ΔP/P ≅ 4x10-8. Observations were not made until several days after each event. This paper reports a third glitch, in 1986 August, detected at Jodrell Bank apparently within 1 hr of the event. This is the first occasion on which the recovery from a glitch in the Crab Pulsar has been observed in detail. The recovery in rotation rate is close to a simple exponential and can be understood in terms of a two-component model of the neutron star. (author)