Plasma distribution functions in accretion onto neutron stars

Previous results for calculations of the plasma distribution function in accretion onto neutron stars which make use of quantum theory are summarized, and possible processes leading to an anisotropic electron distribution function in the "weaker" magnetic field of about 100 million G are investigated using a simpler "classical" theory. The distribution is described by a bi-Maxwellian distribution with different temperatures parallel and perpendicular to the infall direction. The distribution is achieved by conservation of particle magnetic moment about the magnetic field. Excess perpendicular ion energy can be lost to the electrons by Coulomb collisions, and subsequently be radiated away. The implications of the relative sizes of the various Coulomb relaxation times are assessed, and it is concluded that rapid buildup of an inverted population could be preserved for a relatively long time by means of transfer of momentum rather than energy.