Particle acceleration at the magnetic poles of a neutron star

The magnetic conversion of a photon in a neutron-star magnetosphere near one of the magnetic poles is followed by acceleration of the electron and positron to ultra-relativistic energies. The positron moves along open magnetic flux lines to the light cylinder. The electron incident on the stellar surface produces an electromagnetic shower. An order of magnitude estimate has been made of the spectrum of backward-moving photons created in the electron shower. The most important source of photons is shown to be the formation of the giant dipole state in Fe55. Under the assumption that the surface magnetic flux density exceeds 1012G, the photons have, with high probability, mean free paths for magnetic conversion in the magnetosphere of 1 =< lambda =< 104 cm. An equation for the maximum acceleration potential has been obtained in a one-dimensional model of pair creation and electron multiplication based on this photon source. The model has been applied to the phenomenon of subpulse drift in pulsars. The plasma accelerated at the magnetic pole has three components; positrons, protons and light nuclei (Z < approximately 6) formed by spallation, and iron-group nuclei. Equations determining their relative fluxes have been found. The light nuclei include those with Z = 3 to 5, usually considered to be present in galactic cosmic rays only as a result of the interaction of heavier nuclei with the interstellar medium. (author)