The termination shock in a striped pulsar wind

The origin of radio emission from plerions is considered. Recent observations suggest that radio emitting electrons are presently accelerated rather than having been injected at early stages of the plerion evolution. The observed flat spectra without a low frequency cutoff imply an acceleration mechanism that raises the average particle energy by orders of magnitude but leaves most of the particles at the energy less than about few hundred MeV. It is suggested that annihilation of the alternating magnetic field at the pulsar wind termination shock provides the necessary mechanism. Toroidal stripes of opposite magnetic polarity are formed in the wind emanated from an obliquely rotating pulsar magnetosphere (the striped wind). At the termination shock, the flow compresses and the magnetic field annihilates by driven reconnection. Jump conditions are obtained for the shock in a striped wind. It is shown that post-shock MHD parameters of the flow are the same as if the energy of alternating field has already been converted into the plasma energy upstream the shock. Therefore the available estimates of the ratio of the Poynting flux to the matter energy flux, σ, should be attributed not to the total upstream Poynting flux but only to that associated with the average magnetic field. A simple model for the particle acceleration in the shocked striped wind is presented.