Generation of Crab Nebulae Wisps by Plasma Drift Instability

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Abstract
A new mechanism of wisp formation in the Crab Nebula, without recourse to a shock wave, is presented. The mechanism is based on the plasma processes taking place in the relativistic electron-positron plasma, in particular, on excitation of the drift instability in the slightly inhomogeneous magnetic field of the nebula. The magnetic field geometry is assumed to be untwisting spiral-like, concentrated around the rotational equatorial plane of the pulsar. We infer that the energy is transported from the pulsar to the nebula not only by the Poynting flux but also by the kinetic energy of the particles moving along the field lines. We consider a specific relativistic electron-positron plasma with Lorentz factor γ± ~ 10 penetrated by an ion beam with γb ~ 106. It is shown that in such a plasma, taking into account the drift, the generation of low-frequency waves propagating transversely to the magnetic field is possible. In this way the excited Br field causes additional alteration of the magnetic field geometry. The higher luminosity of certain spots is explained by the reorientation of the direction of motion of the synchrotron radiation source (Larmor circle) relative to the observer. The sizes, variability of luminosity, spatial asymmetry, polarization, and transfer velocity, i.e., the main properties of the wisps, are explained. Some predictions are also made.

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