16 research outputs found
The theory of pulsar winds and nebulae
We review current theoretical ideas on pulsar winds and their surrounding
nebulae. Relativistic MHD models of the wind of the aligned rotator, and of the
striped wind, together with models of magnetic dissipation are discussed. It is
shown that the observational signature of this dissipation is likely to be
point-like, rather than extended, and that pulsed emission may be produced. The
possible pulse shapes and polarisation properties are described. Particle
acceleration at the termination shock of the wind is discussed, and it is
argued that two distinct mechanisms must be operating, with the first-order
Fermi mechanism producing the high-energy electrons (above 1 TeV) and either
magnetic annihilation or resonant absorption of ion cyclotron waves responsible
for the 100 MeV to 1 TeV electrons. Finally, MHD models of the morphology of
the nebula are discussed and compared with observation.Comment: 33 pages, to appear in Springer Lecture Notes on "Neutron stars and
pulsars, 40 years after the discovery", ed W.Becke
Pulsar Striped Winds
According to magnetohydrodynamic (MHD) models, the rotational energy of a
rapidly spinning neutron star is carried away by a relativistic wind and
deposited at a large distance, in the nebula, downstream of the wind
termination shock. The energy transport in the outflow is mediated by Poynting
flux, but it is not clear how the energy stored in the fields is transferred
into the energized population of emitting particles. The most plausible
dissipation mechanisms are thought to be related to the "striped" structure of
the wind, in particular, to the existence of a current sheet, prone to
reconnection events. In this model the current sheet is a natural place for
internal dissipation and acceleration of particles responsible for pulsed,
high-energy emission. Moreover, reconnection is a promising scenario for
explaining annihilation of fields at the shock and conversion of their energy
into the kinetic energy of particles. The shock structure, however, is likely
to differ in the low-density plasmas, in which non-MHD effects intervene. In
this regime, the striped wind can dissipate its energy via an electromagnetic
precursor of the shock.Comment: invited review at the Workshop on Modelling Nebulae, June 14-17,
2016, Sant Cugat, Spain; submitted book chapte