Electrodynamics of neutron stars [Review]

摘要

Although the standard model for radio pulsars is a rotating magnetized neutron star and the vast majority (if not all) of pulsars are thought to have appreciable inclination angles between the spin and magnetization axes, most theoretical papers use simplified held models (e.g., aligned spin axis and magnetic dipole axis). Deutsch long ago gave exact tin vacuo) closed expressions for these inclined fields (modulo some typos and oversights), but these expressions were rather clumsy and required extensive hand processing to convert into ordinary functions of radius and angle for the electromagnetic fields. Moreover, these expressions were effectively written down by inspection (no details of the derivations given), which leaves the reader with little physical understanding of where the various electric and magnetic held components come from, particularly near the neutron star surface where many models assume the radio emission is generated. Finally, rather little analysis of what these fields implied was given beyond speculation that they could accelerate cosmic rays. As pulsar models become more sophisticated, it seems important that all researchers use a consistent set of underlying fields, which we hope to present here, as well as understand why these fields are present. It is also interesting to know what happens to charged particles from the star that move in these fields. Close to the star, ambient particles tend to simply E x B drift around the star with the same rotational velocity as the star itself. But far from the star, charged particles are accelerated away in the wave zone, as was first pointed out by Ostriker and Gunn. We expand their calculations using more general fields and elucidate the particle's dynamics accordingly. Very efficient acceleration is observed even for particles starting at > 10(3) light-cylinder distances. We also stress the effects of a non-zero radial magnetic field. Electrons are accelerated to much higher energies than, say, protons (not to the same energy as when the two cross a fixed potential drop). We pay particular attention to particles accelerated along the spin axis (particles that might be involved in jet formation). An important limitation to the present work is the neglect of collective radiation reaction. Single particle radiation reaction (e.g., Compton scattering of the wave flux) is not an accurate estimate of the forces on a plasma. We are working on remedying this limitation. (C) 1999 Elsevier Science B.V. All rights reserved. [References: 37]