Particle acceleration in relativistic current sheets

Abstract

Relativistic current sheets have been proposed as the sites of dissipation in pulsar winds, jets in active galaxies and other Poynting-flux dominated flows. It is shown that the steady versions of these structures differ from their nonrelativistic counterparts because they do not permit transformation to a de Hoffmann/Teller reference frame, in which the electric field vanishes. Instead, their generic form is that of a true neutral sheet: one in which the linking magnetic field component normal to the sheet is absent. Taken together with Alfven's limit on the total cross-field potential, this suggests plasma is ejected from the sheet in the cross-field direction rather than along it. The maximum energy to which such structures can accelerate particles is derived, and used to compute the maximum frequency of the subsequent synchrotron radiation. This can be substantially in excess of standard estimates. In the magnetically driven gamma-ray burst scenario, acceleration of electrons is possible to energies sufficient to enable photon-photon pair production after an inverse Compton scattering event.