Generation of magnetic fluctuations near a shock front in a partially ionized medium

Bykov, A. M.; Топтыгин, И. Н.

doi:10.1134/1.2123289

Cited by 28 publications

(34 citation statements)

References 25 publications

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“…This opens another possibility for the turbulence dissipation to produce an increase in the magnetic field amplification. For instance, Bykov & Toptygin (2005) proposed a mechanism for generating long-wavelength perturbations of magnetic fields by low-energy particles. If such a mechanism is responsible for the generation of a significant fraction of the turbulence that confines the highest energy particles, then the increased particle injection due to the precursor heating may raise the maximum particle energy and, possibly, the value of the amplified magnetic field.…”

Section: Discussionmentioning

confidence: 99%

Turbulence Dissipation and Particle Injection in Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Vladimirov

Bykov²,

Ellison

2008

Astrophysical Journal

111

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The highly amplified magnetic fields suggested by observations of some supernova remnant shells are most likely an intrinsic part of efficient particle acceleration by shocks. This strong turbulence, which may result from cosmicray-driven instabilities, both resonant and nonresonant, in the shock precursor, is certain to play a critical role in selfconsistent, nonlinear models of strong, cosmic-ray-modified shocks. Here we present a Monte Carlo model of nonlinear diffusive shock acceleration (DSA) accounting for magnetic field amplification through resonant instabilities induced by accelerated particles, and including the effects of dissipation of turbulence upstream of a shock and the subsequent precursor plasma heating. Feedback effects between the plasma heating due to turbulence dissipation and particle injection are strong, adding to the nonlinear nature of efficient DSA. Describing the turbulence damping in a parameterized way, we reach two important results: first, for conditions typical of supernova remnant shocks, even a small amount of dissipated turbulence energy ($10%) is sufficient to significantly heat the precursor plasma; and second, the heating upstream of the shock leads to an increase in the injection of thermal particles at the subshock by a factor of several. In our results, the response of the nonlinear shock structure to the boost in particle injection prevented the efficiency of particle acceleration and magnetic field amplification from increasing. We argue, however, that more advanced (possibly nonresonant) models of turbulence generation and dissipation may lead to a scenario in which particle injection boost due to turbulence dissipation results in more efficient acceleration and even stronger amplified magnetic fields than without the dissipation.

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Section: Discussionmentioning

confidence: 99%

Turbulence Dissipation and Particle Injection in Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Vladimirov

Bykov²,

Ellison

2008

Astrophysical Journal

111

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“…Blandford & Ostriker (1980) considered an ISM made of cleared hot cavities from supernovae and showed how the resulting shocks could scatter and accelerate cosmic rays. Bykov & Toptygin (1985) extended this model to include secondary shocks that arise in the turbulence caused by the supernovae. Klepach, Ptuskin & Zirakashvili (2000) included stellar wind shocks.…”

Section: Other Scattering Mechanismsmentioning

confidence: 99%

Interstellar Turbulence II: Implications and Effects

Scalo

Elmegreen

2004

Annu. Rev. Astron. Astrophys.

308

157

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Interstellar turbulence has implications for the dispersal and mixing of the elements, cloud chemistry, cosmic ray scattering, and radio wave propagation through the ionized medium. This review discusses the observations and theory of these effects. Metallicity fluctuations are summarized, and the theory of turbulent transport of passive tracers is reviewed. Modeling methods, turbulent concentration of dust grains, and the turbulent washout of radial abundance gradients are discussed. Interstellar chemistry is affected by turbulent transport of various species between environments with different physical properties and by turbulent heating in shocks, vortical dissipation regions, and local regions of enhanced ambipolar diffusion. Cosmic rays are scattered and accelerated in turbulent magnetic waves and shocks, and they generate turbulence on the scale of their gyroradii. Radio wave scintillation is an important diagnostic for small scale turbulence in the ionized medium, giving information about the power spectrum and amplitude of fluctuations. The theory of diffraction and refraction is reviewed, as are the main observations and scintillation regions.

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“…Recently, Bykov & Toptygin (2005), have investigated a similar instability to that in Bell (2004), driven by a neutralising return current in the thermal background plasma, in a partially ionised medium. A single fluid MHD description of the background particles with a generalised Ohm's law is used, and the cosmic ray current is found by solving the kinetic transport equation.…”

Section: Introductionmentioning

confidence: 99%

A cosmic ray current-driven instability in partially ionised media

Reville¹,

Kirk²,

Duffy³

et al. 2007

A&A

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Context. We investigate the growth of hydromagnetic waves driven by streaming cosmic rays in the precursor environment of a supernova remnant shock. Aims. It is known that transverse waves propagating parallel to the mean magnetic field are unstable to anisotropies in the cosmic ray distribution, and may provide a mechanism to substantially amplify the ambient magnetic field. We quantify the extent to which temperature and ionisation fractions modify this picture. Methods. Using a kinetic description of the plasma we derive the dispersion relation for a collisionless thermal plasma with a streaming cosmic ray current. Fluid equations are then used to discuss the effects of neutral-ion collisions. Results. We calculate the extent to which the environment into which the cosmic rays propagate influences the growth of the magnetic field, and determines the range of possible growth rates. Conclusions. If the cosmic ray acceleration is efficient, we find that very large neutral fractions are required to stabilise the growth of the non-resonant mode. For typical supernova parameters in our Galaxy, thermal effects do not significantly alter the growth rates. For weakly driven modes, ion-neutral damping can dominate over the instability at more modest ionisation fractions. In the case of a supernova shock interacting with a molecular clouds, such as in RX J1713.7-3946, with high density and low ionisation, the modes can be rapidly damped.

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Generation of magnetic fluctuations near a shock front in a partially ionized medium

Cited by 28 publications

References 25 publications

Turbulence Dissipation and Particle Injection in Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Turbulence Dissipation and Particle Injection in Nonlinear Diffusive Shock Acceleration with Magnetic Field Amplification

Interstellar Turbulence II: Implications and Effects

A cosmic ray current-driven instability in partially ionised media

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