Escape of high-energy particles from bow-shock pulsar wind nebulae

Abstract

The detection of bright X-ray features and large TeV halos around old pulsars that have escaped their parent Supernova Remnants and are interacting directly with the ISM, suggest that high energy particles, more likely high energy pairs, can escape from these systems, and that this escape if far more complex than a simple diffusive model can predict. Here we present for the first time a detailed analysis of how high energy particles escape from the head of the bow shock. In particular we focus our attention on the role of the magnetic field geometry, and the inclination of the pulsar spin axis with respect to the direction of the pulsar kick velocity. We show that asymmetries in the escape pattern of charged particles are common, and they are strongly energy dependent. More interestingly we show that the flow of particles from bow-shock pulsar wind nebulae is likely to be charge separated, which might have profound consequences on the way such flow interacts with the ISM magnetic field, driving local turbulence.