Le 5 octobre 2012
À 10h30
Salle de Cours – Grande Coupole
Iwona MOCHOL
MPIK Heidelberg, Allemagne
Fast spinning, highly magnetized neutron stars deposit their rotational energy in a relativistic wind. This outflow is a mixture of plasma, produced close to the star, and strong electromagnetic fields that are anchored in its surface and twisted beyond the light cylinder. The energy transfer is mediated by the fields, and is usually modelled using the equations of relativistic magnetohydrodynamics (MHD). However, at large distance from the source the outflowing plasma becomes diluted so that the MHD approach is not appropriate any longer, and the propagation of nonlinear electromagnetic (EM) waves becomes possible. These modes can be described within the two-fluid (electron-positron) model of a cold plasma. They impart relativistic speeds on the particles, effectively transferring the energy stored in the fields to the medium. This property can explain a puzzle how the wind evolves from a strongly Poynting-flux dominated regime at launch, to a weakly magnetized, particle-dominated nebula, present downstream of the shock where the pulsar wind is terminated. Here we discuss the role of a strong EM wave in the formation of this shock. In particular, we analyze its radial propagation characteristics, and possible damping caused by the radiation reaction of emitting particles. We discuss new self-consistent solutions, in which the wave is asymptotically matched to constant pressure surroundings, and the observational consequences for both isolated pulsars, and pulsars in binary systems.