Pulsar bow-shock nebulae

Abstract

Pulsar bow-shock nebulae originate from the interaction of the ambient medium with the wind of a moving pulsar. The properties of these nebulae depend on both the physical conditions in the ambient medium and the characteristics of the pulsar wind, and may thus represent a powerful diagnostic tool. The main limits to this study are, on the observational side, the very limited sample of pulsar bow-shock nebulae known so far and, on the theoretical one, a still limited understanding of the physical conditions in these nebulae: in particular, classical bow-shock models are not appropriate to describe these objects. In this paper we outline the most likely physical regimes for nebulae associated with typical pulsars, and discuss why classical models cannot be applied to these objects. We also discuss how microphysical processes may aect both the dynamics of the flow and the properties of the emission (mostly in Balmer lines). We nally put forward a criterion to select among the known pulsars those with the highest probability of having a detectable bow-shock nebula.