Revised Pulsar Spin‐down

We address the issue of electromagnetic pulsar spindown by combining ourexperience from the two limiting idealized cases which have been studied ingreat extent in the past: that of an aligned rotator where ideal MHD conditionsapply, and that of a misaligned rotator in vacuum. We construct a spindownformula that takes into account the misalignment of the magnetic and rotationaxes, and the magnetospheric particle acceleration gaps. We show that near thedeath line aligned rotators spin down much slower than orthogonal ones. Inorder to test this approach, we use a simple Monte Carlo method to simulate theevolution of pulsars and find a good fit to the observed pulsar distribution inthe P-Pdot diagram without invoking magnetic field decay. Our model may alsoaccount for individual pulsars spinning down with braking index n < 3, byallowing the corotating part of the magnetosphere to end inside the lightcylinder. We discuss the role of magnetic reconnection in determining thepulsar braking index. We show, however, that n ~ 3 remains a good approximationfor the pulsar population as a whole. Moreover, we predict that pulsars nearthe death line have braking index values n > 3, and that the older pulsarpopulation has preferentially smaller magnetic inclination angles. We discusspossible signatures of such alignment in the existing pulsar data.Comment: 8 pages, 7 figures; accepted to Ap