Implications of H.E.S.S. observations of pulsar wind nebulae

TL;DR

This review discusses the properties, evolution, and magnetic field estimates of pulsar wind nebulae, especially those observed by H.E.S.S., highlighting the leptonic interpretation of Vela X and the impact of inhomogeneous interstellar medium on nebula morphology.

Contribution

It provides a comprehensive framework for interpreting offset pulsar wind nebulae observed by H.E.S.S., incorporating recent observational and theoretical insights.

Findings

Leptonic interpretation is favored for Vela X H.E.S.S. signal.

Inhomogeneous interstellar medium influences nebula morphology.

Constraints on particle energetics and magnetic fields are established.

Abstract

In this review paper on pulsar wind nebulae (PWN) we discuss the properties of such nebulae within the context of containment against cross-field diffusion (versus normal advection), the effect of reverse shocks on the evolution of offset ``Vela-like'' PWN, constraints on maximum particle energetics, magnetic field strength estimates based on spectral and spatial properties, and the implication of such field estimates on the composition of the wind. A significant part of the discussion is based on the High Energy Stereoscopic System ({\it H.E.S.S.} or {\it HESS}) detection of the two evolved pulsar wind nebulae Vela X (cocoon) and HESS J1825-137. In the case of Vela X (cocoon) we also review evidence of a hadronic versus a leptonic interpretation, showing that a leptonic interpretation is favored for the {\it HESS} signal. The constraints discussed in this review paper sets a general framework for the interpretation of a number of offset, filled-center nebulae seen by {\it HESS}. These sources are found along the galactic plane with galactic latitudes $|b|\sim 0$, where significant amounts of molecular gas is found. In these regions, we find that the interstellar medium is inhomogeneous, which has an effect on the morphology of supernova shock expansion. One consequence of this effect is the formation of offset pulsar wind nebulae as observed.