Review of the theory of pulsar‐wind nebulae

Abstract

Pulsar-wind nebulae (PWNe) are ideal astrophysical laboratories where high energy relativistic phenomena can be investigated. They are close, well resolved in our observations, and the knowledge derived in their study has a strong impact in many other fields, from AGNs to GRBs. Yet there are still unresolved issues, that prevent us from a full clear understanding of these objects. The lucky combination of high resolution X-ray imaging and numerical codes to handle the outflow and dynamical properties of relativistic MHD, has opened a new avenue of investigation that has lead to interesting progressed in the last years. Despite all of these, we do not understand yet how particles are accelerated, and the functioning of the pulsar wind and pulsar magnetosphere, that power PWNe. I will review what is now commonly known as the MHD paradigm, and in particular I will focus on various approaches that have been and are currently used to model these systems. For each I will highlight its advantages and limitations, and degree of applicability.

Pulsar Wind Nebulae with Bow Shocks: Non-thermal Radiation and Cosmic Ray Leptons

“…The modeling of the structure of PWNe interacting with supersonic flows either inside or outside of supernova remnants with an adequate account for the magnetic field structure is a complicated problem (see, e.g., Blondin et al 2001, Bucciantini and Bandiera 2001, Bucciantini 2014). The study of particle transport in these systems faces the complexities related to a non-trivial behaviour of magnetized flows in the vicinity of the contact discontinuity.…”

“…Bow-shock nebulae are known to originate from the interaction of winds from moving stars with the ambient medium and appear in association with very different types of stars: of solar type (see, e.g., Baranov et al 1971), young massive stars (see, e.g., Weaver et al 1977), and fast rotating magnetized neutron stars (see, e.g., Bucciantini andBandiera 2001, Blondin et al 2001). The dynamics of astrophysical bow shocks has been modelled both analytically, within the thin shell approximation, and by means of numerical hydrodynamics schemes (see, e.g., Bandiera 1993, Wilkin 1996.…”

Shock structures of astrospheres

“…The problem with these models is that the electrons are important for the heat transfer. The behavior of the electrons is not well understood at the termination shock and beyond, but see Chashei & Fahr (2013, 2014. For O star astrospheres, Arthur (2007) included a heat transfer model to avoid too strong adiabatic cooling of the stellar wind at the TS.…”

“…Therefore, we no longer distinguish between different astrospheres (Arthur 2007(Arthur , 2012, pulsar wind nebulae (Bucciantini 2002(Bucciantini , 2014 or the heliosphere, as long as we can describe them by a single collisionless fluid without other interactions. In that sense, this section is generally applicable to all single-fluid astrospheres.…”

Cascades and Dissipative Anomalies in Compressible Fluid Turbulence

“…Compressible fluids play a vital role in problems of astrophysics (interstellar medium [1], star-formation [2,3]), applied physics (inertial confinement fusion [4]), and engineering (high-temperature reactive flows [5], supersonic aircraft design [6]). Relativistic fluids are necessarily compressible, of course, and occur in astrophysical flows (pulsars [7], gamma-ray bursts [8]), high-energy physics (heavy-ion collisions [9]), and condensed matter physics (graphene [10][11][12], strange metals [13,14]). In many of the above examples the fluid is either directly observed or indirectly inferred to be in a turbulent state.…”