Magnetic and density spikes in cosmic ray shock precursors

Abstract

In shock precursors populated by accelerated cosmic rays (CR), the CR return current instability is believed to significantly enhance the pre-shock perturbations of magnetic field. We have obtained fully-nonlinear exact ideal MHD solutions supported by the CR return current. The solutions occur as localized spikes of circularly polarized Alfven envelopes (solitons, or breathers). As the conventional (undriven) solitons, the obtained magnetic spikes propagate at a speed $C$ proportional to their amplitude, $C=C_A{B}_{\max }/\sqrt{2}{B}_0$. The sufficiently strong solitons run thus ahead of the main shock and stand in the precursor, being supported by the return current. This property of the nonlinear solutions is strikingly different from the linear theory that predicts non-propagating (that is, convected downstream) circularly polarized waves. The nonlinear solutions may come either in isolated pulses (solitons) or in soliton-trains (cnoidal waves). The morphological similarity of such quasi-periodic soliton chains with recently observed X-ray stripes in Tycho supernova remnant (SNR) is briefly discussed. The magnetic field amplification determined by the suggested saturation process is obtained as a function of decreasing SNR blast wave velocity during its evolution from the ejecta-dominated to the Sedov-Taylor stage.

21 pages, 4 figures

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Cited by in corpus (7)

• Diffusive shock acceleration and magnetic field amplification
• Origin of Cosmic Rays
• Microphysics of cosmic ray driven plasma instabilities
• Magnetic field amplification in nonlinear diffusive shock acceleration including resonant and non-resonant cosmic-ray driven instabilities
• Collisionless shocks in partly ionized plasma with cosmic rays: microphysics of non-thermal components
• Wave Propagation at Oblique Shocks: How Did Tycho Get Its Stripes?
• Radio polarization maps of shell-type SNRs II. Sedov models with evolution of turbulent magnetic field