Cosmic-Ray Streaming Perpendicular to the Mean Magnetic Field

Forman, M. A.; Jokipii, J. R.; Owens, A. J.

doi:10.1086/153087

Cited by 160 publications

(90 citation statements)

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“…Beginning in the 1960 s, the astrophysics and space physics communities devoted considerable effort to studying the propagation of test particles in random magnetic fields [31][32][33][34] with the goal of relating the spatial spreading of cosmic rays to statistical descriptions of fieldline wandering. In the limit that cosmic rays follow the fieldlines, they can wander perpendicular to the mean magnetic field no faster than the fieldlines themselves wander with respect to the mean.…”

Section: A Fieldline Geometrymentioning

confidence: 99%

The microphysics and macrophysics of cosmic rays

2013

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This review paper commemorates a century of cosmic ray research, with emphasis on the plasma physics aspects. Cosmic rays comprise only ∼10−9 of interstellar particles by number, but collectively their energy density is about equal to that of the thermal particles. They are confined by the Galactic magnetic field and well scattered by small scale magnetic fluctuations, which couple them to the local rest frame of the thermal fluid. Scattering isotropizes the cosmic rays and allows them to exchange momentum and energy with the background medium. I will review a theory for how the fluctuations which scatter the cosmic rays can be generated by the cosmic rays themselves through a microinstability excited by their streaming. A quasilinear treatment of the cosmic ray–wave interaction then leads to a fluid model of cosmic rays with both advection and diffusion by the background medium and momentum and energy deposition by the cosmic rays. This fluid model admits cosmic ray modified shocks, large scale cosmic ray driven instabilities, cosmic ray heating of the thermal gas, and cosmic ray driven galactic winds. If the fluctuations were extrinsic turbulence driven by some other mechanism, the cosmic ray background coupling would be entirely different. Which picture holds depends largely on the nature of turbulence in the background medium.

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Section: A Fieldline Geometrymentioning

confidence: 99%

The microphysics and macrophysics of cosmic rays

2013

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“…Transport perpendicular to the field is then governed by a kinetic theory description, so that the ratio of the spatial diffusion coefficients parallel (κ || = λv/3) and perpendicular (κ ⊥ ) to the magnetic field is given by κ ⊥ /κ || = 1/(1 + η 2 ) (see Forman et al 1974;Ellison et al 1995 for detailed expositions). Hence, η couples directly to the amount of cross-field diffusion and is a measure of the level of turbulence in the system, i.e., is an indicator of δB/B .…”

Section: The Monte Carlo Simulation Techniquementioning

confidence: 99%

“…In the event that acceleration time information is needed, a retrodictive approach described first in Jones (1978) and later applied directly to a Monte Carlo simulation in Ellison et al (1990a) can be used. One important finding is that the interplay between energy boosting and time dilation effects leads only to modest changes (Baring 2002) in the acceleration time at plane-parallel relativistic shocks compared with standard non-relativistic shock formalism (Forman et al 1974). The consideration of particle acceleration times is beyond the scope of the present work and will be deferred to a future investigation.…”

Section: The Monte Carlo Simulation Techniquementioning

confidence: 99%

Diffusive Acceleration of Particles at Oblique, Relativistic, Magnetohydrodynamic Shocks

Summerlin

Baring

2011

ApJ

162

233

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Diffusive shock acceleration (DSA) at relativistic shocks is expected to be an important acceleration mechanism in a variety of astrophysical objects including extragalactic jets in active galactic nuclei and gamma-ray bursts. These sources remain good candidate sites for the generation of ultrahigh energy cosmic rays. In this paper, key predictions of DSA at relativistic shocks that are germane to the production of relativistic electrons and ions are outlined. The technique employed to identify these characteristics is a Monte Carlo simulation of such diffusive acceleration in test-particle, relativistic, oblique, magnetohydrodynamic (MHD) shocks. Using a compact prescription for diffusion of charges in MHD turbulence, this approach generates particle angular and momentum distributions at any position upstream or downstream of the shock. Simulation output is presented for both small angle and large angle scattering scenarios, and a variety of shock obliquities including superluminal regimes when the de Hoffmann-Teller frame does not exist. The distribution function power-law indices compare favorably with results from other techniques. They are found to depend sensitively on the mean magnetic field orientation in the shock, and the nature of MHD turbulence that propagates along fields in shock environs. An interesting regime of flat-spectrum generation is addressed; we provide evidence for it being due to shock drift acceleration, a phenomenon well known in heliospheric shock studies. The impact of these theoretical results on blazar science is outlined. Specifically, Fermi Large Area Telescope gamma-ray observations of these relativistic jet sources are providing significant constraints on important environmental quantities for relativistic shocks, namely, the field obliquity, the frequency of scattering, and the level of field turbulence.

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“…According to current theoretical understanding, cosmic rays at neutron monitor energies are in the "weak-scattering" regime, where fluxes driven by perpendicular diffusion are small compared to those driven by "B x Vn" drift [Forman et al, 1974;Bieber and Matthaeus, 1997]. Based on these considerations, we conclude that the enhanced anisotropies observed before and during the January 1997 CME were predominantly a result of B x Vn drift flux driven by gradients perpendicular to the field.…”

Section: Cosmic Ray Density Gradientsmentioning

confidence: 61%

CME geometry in relation to cosmic ray anisotropy

Bieber¹,

Evenson²

1998

Geophysical Research Letters

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Abstract. Strong enhancements of the cosmic ray anisotropy were observed before and during the January 1997 CME/ magnetic cloud. From a multi-station analysis of neutron monitor data, we conclude that "B x •7n" drift is a primary source of CME-related anisotropies for 5 GeV cosmic rays. Evolution of the cosmic ray density and density gradients is closely linked to magnetic properties of the ejecta, and provides information on the magnetic cloud and related features as they approach and pass Earth. Strong enhancement of the field-aligned anisotropy was observed primarily during the 9 hours prior to shock arrival. If typical, this phenomenon should prove useful for space weather forecasting.

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Cosmic-Ray Streaming Perpendicular to the Mean Magnetic Field

Cited by 160 publications

References 0 publications

The microphysics and macrophysics of cosmic rays

The microphysics and macrophysics of cosmic rays

Diffusive Acceleration of Particles at Oblique, Relativistic, Magnetohydrodynamic Shocks

CME geometry in relation to cosmic ray anisotropy

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