New insights into the physics of bow shock nebulae through numerical simulations

Pulsars moving supersonically are known to give rise to the formation of cometary-like nebulae known as Pulsar Bow Shock Nebulae. These originate from the confinement of the relativistic pulsar wind by the ram pressure of the ambient medium through which the star is moving. If the external medium is the ISM, such nebulae might be observed through Balmer emission, due to the interaction of the incoming neutrals with the outer layer of shocked ISM. In this case simple analytic models can provide a reasonable description of the nebular structure and emission properties. However, recent observational progress has shown the presence of non-thermal emission both in the radio and X-ray bands. This is thought to be associated with the plasma heated to relativistic temperatures at the pulsar wind termination shock, and flowing in the inner parts of the nebula. Interestingly, there is evidence that this emission is structured, and it does not seem to be easily interpretable within simplified models. A new effort at modeling these regions is thus necessary in order to derive from the observed features physical insight into the properties of these objects. Here we present the results of a study of the flow structure in pulsar bow shock nebulae by means of numerical simulations. The simulations are performed, for the first time, in the proper relativistic MHD regime. Synchrotron emission maps are also derived.