Nonthermal origin of X-rays from rotation-powered neutron stars

Abstract

We propose that the bulk of X-rays observed in pulsars results from the synchrotron radiation of e ± pairs created in strong pulsar magnetic field near the neutron star surface by curvature photons emitted by charged particles on their way from the outer gap to the neutron star surface. The characteristic energy of these curvature photons is completely determined by the size of the outer gap, which is self-consistently limited by thermal X-rays from the neutron star surface heated by the backflow electrons/positrons from the outer gap. It is this limitation of the outer gap size (potential drop) that constrains the luminosity L x of the synchrotron X-rays emitted by a pulsar to about 0.1% of its spin-down power L sd. © 1998. The American Astronomical Society. All rights reserved.