Pulsar magnetogyro ratios and pulsar evolution. IV. Peaks in the pulse period number density distribution, and short-period evolution

The model of pulsar evolution that assumes fossil magnetic fields for pulsars that decay with a time constant of about nine million yr is examined to see if it is compatible with the bimodal pulse period number density distribution found in the distance-restricted pulsar sample. It is shown that the ad hoc assumption of two classes of pulsars must be adopted if the fossil field model is to be preserved, whereas the second peak in the distribution is predicted by the gamma-constant/enhancement model of pulsar evolution. A Monte Carlo simulation based on the standard model is carried out to test the viability of the standard model for short-period pulsars. The evolution of short-period pulsars elicited by the imposition of radio luminosity selection criteria is shown to conform to the gamma-constant/enhancement model. 8 references