Theory of pulsars - Polar caps, sparks, and coherent microwave radiation

Abstract

Several consequences are derived for a neutron star whose magnetic moment tends to be antiparallel to its spin angular momentum, when emitted electrons do not return to the star through the light cylinder along the open field lines. A polar magnetospheric gap is formed that spans the open field lines from the stellar surface up to an altitude of about 10,000 cm. The scalar product of the electric and magnetic fields is nonzero in the gap, although it vanishes essentially everywhere else in the near magnetosphere. The potential difference between the base and the top of the gap is about 1 trillion volts. The gap continually breaks down by forming electron-positron pairs on a time scale of a few microseconds. The gap positrons move out along the open field lines and electrons flow to the stellar surface to close the pulsar's homopolar generator circuit. The proposed model can explain many characteristics of the coherent microwave radiation observed from pulsars.