Bow Shock Pulsar Wind Nebulae

Bow shock Pulsar Wind Nebulae (BSPWNe) form when a fast moving pulsar interact with the ambient medium, after having leaved

At the same time more refined diagnostics for the evolution of the accelerated particles is being implemented, and a special attention is planned to be devoted, as already in the past, to time-variability in the inner nebula. Our final purpose is that of using all the information available from observations to clarify the most fascinating aspects of PWN physics: the composition, in terms of particles and fields, of the wind that emanates from the pulsar magnetosphere and what the particle acceleration mechanism is at the pulsar wind termination shock, a shock that should not be accelerating particles at all according to our standard theories and is proven to be instead one of the best accelerators in the Universe.

Aside from explaining how particles are accelerated in these nebulae, another increasingly hot topic has to do with their release in the ISM. The excess of cosmic ray positrons measured by PAMELA and AMS02 has prompted to consider pulsars as possible contributing sources. Since alternative scenarios either include a radical change in our view of Cosmic Ray origin or propagation, or interpret the excess as a signature of Dark Matter related processes, assessing the pulsar contribution to this excess is particularly topical. Our group has developed pulsar based models for the origin of the positron excess that assume that the particles we see are accelerated at PWN shocks, with the typical flat spectrum that we deduce from observations of these objects in the radio band, and are only released in the ISM when the pulsar exits the parent supernova remnant. Pulsars are a population with high proper velocities and when they leave their parent SNR often find themselves moving in the ISM with supersonic speed: this gives rise to the so-called Pulsar Bow Shock Nebulae observed in radio, X-ray and Hα emission.