Millisecond Pulsar Alignment: PSR J0437−4715

Abstract

The abundances of both orthogonal and nearly aligned neutron stars among the disk population millisecond pulsars appear to be excessively large, relative to those of canonical pulsars. Both of these excesses are expected in strongly spun-up neutron stars. Their surface magnetic field evolution mirrors the changes in the core magnetic field configuration caused by the strong interaction between a core's spinning-up superfluid neutrons and its magnetized superconducting protons. We discuss special observable properties of such a nearly aligned millisecond pulsar and propose an explanation of the apparent paradox for interpreting observations of the very close millisecond pulsar PSR J0437-4715: a strongly modulated X-ray light curve and an extraordinarily broad radio-pulse structure that covers more than three-fourths of the spin period. The former is usually associated with emission polar caps that are being eclipsed by the star's own rotation, while the latter strongly supports alignment and a viewing angle that allows uninterrupted observation of the polar cap.