Cosmic-Ray Propagation in the Galaxy: Collective Effects

Wentzel, Donat G.

doi:10.1146/annurev.aa.12.090174.000443

Cited by 332 publications

(229 citation statements)

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“…Collimation is further limited by the beam instability to growing Alfvén waves. If the instability occurs, the protons become nearly isotropic and propagate parallel to the magnetic field with a mean velocity of the Alfvén speed (Wentzel 1974).…”

Section: Discussionmentioning

confidence: 99%

Absence of linear polarization in Hαemission of solar flares

Bianda

Benz

Stenflo

et al. 2005

A&A

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Abstract. High sensitivity observations of Hα polarization of 30 flares of different sizes and disk positions are reported. Both filter and spectrographic techniques have been used. The ZIMPOL system eliminates spurious polarizations due to seeing and flat-field effects. We didn't find any clear linear polarization signature above our sensitivity level which was usually better than 0.1%. The observations include an X17.1 flare with gamma-ray lines reported by the RHESSI satellite. These results cast serious doubts on previous claims of linear polarization at the one percent level and more, attributed to impact polarization. The absence of linear polarization limits the anisotropy of energetic protons in the Hα emitting region. The likely causes are isotropization by collisions with neutrals in the chromosphere and defocusing by the converging magnetic field.

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Section: Discussionmentioning

confidence: 99%

Absence of linear polarization in Hαemission of solar flares

Bianda

Benz

Stenflo

et al. 2005

A&A

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“…The chief objection to this interpretation is that the strong anisotropy of the supercoherent mode might be rapidly attenuated by the collective effects reviewed by Wentzel (1974). However, the conventional view, that· these wave effects limit streaming velocities to the Alfven velocity,applies to steady state conditions.…”

Section: • the Supercoherent Modementioning

confidence: 99%

The effect of adiabatic focusing upon charged-particle propagation in random magnetic fields

Earl¹

1976

ApJ

152

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“…Extragalactic magnetic field strengths and coherence lengths are not well established, but it may be plausible to assume a Kolmogorov form for the turbulent magnetic field power spectrum with coherent directions on scales of 0.5 -1 Mpc. One can then naïvely estimate that protons with energies E < 10 21 ℓ Mpc B µG eV remain trapped inside magnetic subdomains of size ℓ, attaining efficient diffusion when the wave number of the associated Alfvén wave is equal to the gyroradius of the particle [28]. With a Kolmogorov spectrum this gives for a diffusion coefficient [29] D…”

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confidence: 99%

Auger Test of the Cen A Model of Highest Energy Cosmic Rays

Anchordoqui

Goldberg²,

Weiler³

2001

Phys. Rev. Lett.

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If, as recently proposed by Farrar and Piran, Cen A is the source of cosmic rays detected above the Greisen-Zatsepin-Kuz'min cutoff, neutrons are ≈ 140 more probable than protons to be observed along its line of sight. This is because the proton flux is rendered nearly isotropic by O(µG) intergalactic magnetic fields. With the anticipated aperture of the Southern Auger Observatory, one may expect on the order of 2 neutron events/year above 10 20 eV in the line of sight of Cen A.The energy spectrum of cosmic rays (CRs) is well fitted by power laws with increasing index for energies above 4 × 10 15 eV (the "knee") flattening again above 5 × 10 18 eV (the "ankle"), yielding the overall shape of a leg. Over the last third of the century, ingenious installations with large effective areas and long exposure times-needed to overcome the steep falling flux-have raised the tail of the spectrum up to an energy of 3 × 10 20 eV, with no evidence that the highest energy recorded thus far is Nature's upper limit [1]. The origin of these extraordinarily energetic particles continues to present a major enigma to high energy physics [2].The main problem posed by the detection of CRs of such energy (if nucleons, gammas, and/or nuclei) is energy degradation through inelastic collisions with the universal radiation fields permeating the universe. Therefore, if the CR sources are all at cosmological distances, the observed spectrum must virtually end with the Greisen-Zatsepin-Kuz'min (GZK) cutoff at E ≈ 8 × 10 19 eV [3]. The spectral cutoff is less sharp for nearby sources (within 50 Mpc or so). The arrival directions of the trans-GZK events are distributed widely over the sky, with no plausible counterparts (such as sources in the Galactic Plane or in the Local Supercluster). Furthermore, the data are consistent with an isotropic distribution of sources in sharp constrast to the anisotropic distribution of light within 50 Mpc [4]. The difficulties encountered by conventional acceleration mechanisms in accelerating particles to the highest observed energies have motivated suggestions that the underlying production mechanism could be of non-acceleration nature. Namely, charged and neutral primaries, mainly light mesons (pions) together with a small fraction (3%) of nucleons, might be produced at extremely high energy by decay of supermassive elementary X particles (m X ∼ 10 22 − 10 28 eV) [5]. However, if this were the case, the observed spectrum should be dominated by gamma rays and neutrinos, in contrast to current observation [6]! Alternative explanations involve undiscovered neutral hadrons with masses above a few GeV [7], neutrinos producing nucleons and photons via resonant Z-production with the relic neutrino background [8], or else neutrinos attaining cross sections in the millibarn range above the electroweak scale [9]. A controversial correlation between the arrival direction of CRs above 10 20 eV and high redshift compact radio quasars seems to support these scenarios [10].Over the last few years, it has become evident tha...

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Cosmic-Ray Propagation in the Galaxy: Collective Effects

Cited by 332 publications

References 0 publications

Absence of linear polarization in Hαemission of solar flares

Absence of linear polarization in Hαemission of solar flares

The effect of adiabatic focusing upon charged-particle propagation in random magnetic fields

Auger Test of the Cen A Model of Highest Energy Cosmic Rays

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