Proton transport through self-generated waves in impulsive flares

Vainio, R.; Kocharov, L. G.

doi:10.1051/0004-6361:20010846

Cited by 9 publications

(7 citation statements)

References 19 publications

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“…(Note, however, that in case of active regions, n can be two orders of magnitude larger than the adopted value). A similar analytical estimate for negligible wave growth was shown to agree with time-dependent simulations by Vainio & Kocharov (2001) in case of proton transport through self-generated waves in flaring coronal loops.…”

Section: Wave Growth Between the Sun And 1 Ausupporting

confidence: 73%

On the generation of Alfvén waves by solar energetic particles

Vainio

2003

A&A

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Abstract.A simple analytical theory of Alfvén waves amplified by streaming solar energetic particles (SEPs) is studied. It is pointed out that a finite time-integrated net flux of energetic protons has to pass each point in space before we can expect Alfvén waves to be significantly modified by the streaming instability. The time-integrated net proton flux needed for the time-integrated wave growth rate (or wave growth, for short) to exceed unity is evaluated. Assuming that protons stream much faster than the waves, we evaluate the wave growth as a function of position and wavenumber for a specified proton injection energy spectrum, dN/dE. The wave growth is found to be proportional to vp dN/dE, where v and p are the particle speed and momentum, and to the local Alfvén speed V A . Thus, maximum wave growth is achieved at the location of maximum V A (at a few solar radii), and the minimum value of dN/dE required for the wave growth to exceed unity there is a few times 10 32 /vp protons per unit solid angle (in coordinate space) at the solar surface. If dN/dE is below this value, test-particle theory is a valid description of particle transport and acceleration. The value is not exceeded (above 1 MeV energies) in small gradual SEP events having peak 1-MeV proton intensities below ∼10 protons (cm 2 sr s MeV) −1 at 1 AU. The spatial and momentum dependence of the wave growth can also be used to estimate the maximum emission strength of a moving proton source in the interplanetary medium. For a strong source moving through the solar wind at constant super-Alfvénic speed, the number of escaping particles per unit time and flux-tube cross section is approximately constant in time, predicting a plateau-type timeintensity profile observed ahead of the source. The model reproduces observations of streaming-limited intensities at energies around 10 MeV and explains the double peaked injection profiles observed in large SEP events.

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Section: Wave Growth Between the Sun And 1 Ausupporting

confidence: 73%

On the generation of Alfvén waves by solar energetic particles

Vainio

2003

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“…due to a high level of turbulence close to the Sun, as suggested, e.g. in the model by Vainio and Kocharov (2001). Nonetheless, particle acceleration to GeV energies must be fast and must occur only close to the Sun, because particle intensities at these energies decay fast.…”

Section: Continuation To Higher Energiesmentioning

confidence: 87%

“…This small ratio does not necessarily indicate particle acceleration in closed loops, in particular since the timescales of curvature drift are too long to explain the observed particle escape (Ramaty and Mandzhadvidze 1994). Instead, it can be interpreted in terms of a primarily downward accelerated isotropic particle distribution (Share et al 2002) or from acceleration on open field lines with the bulk of the particles trapped in self-generated turbulence (Vainio and Kocharov 2001). However, the escape of only a small part of the flare-accelerated particles is sufficient to cause a significant particle event in interplanetary space.…”

Section: Interacting and Escaping Particlesmentioning

confidence: 95%

Current views on impulsive and gradual solar energetic particle events

Kallenrode

2003

J. Phys. G: Nucl. Part. Phys.

132

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Solar energetic particles (SEPs) are one manifestation of violent energy releases on the Sun. The study of their acceleration and propagation reveals information about basic plasma-physical processes, such as reconnection, shock acceleration and wave-particle interaction, in astrophysical objects, such as stars, magnetospheres or the diluted plasma of the interstellar or interplanetary medium. This paper introduces the current classification scheme for solar energetic particle events, its relation to the underlying acceleration processes, and addresses open questions regarding the better understanding of SEPs as well as the underlying physical processes. Modifications to the current paradigm considering more recent observations will be suggested.

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“…Eventually, one has to drop the assumption of a steady state and to address the problem in a time-dependent manner. This can probably only be done via numerical simulations, for which a number of tools are already under development (see, e.g., Vainio & Kocharov 2001;Vainio 2002 …”

Section: Discussionmentioning

confidence: 99%

Conversion of bulk kinetic energy into radiation in AGNs and GRBs: Particle transport effects

Vainio

Pohl

Schlickeiser

2004

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Abstract. We investigate the spatial structure of collisionless collision fronts in relativistic outflows interacting with ambient material. As a result of the interaction, ambient particles are picked up by the outflow and generate transverse plasma waves via streaming instabilities. Pick-up particle transport under the influence of self-generated turbulence inside such interaction regions is studied. We extend our previous momentum space modeling to include also a spatial dimension. We find that the following possibilities are consistent with quasi-linear equations of particle transport and wave generation: (i) if background waves have small intensities inside the outflow region, leading to inefficient scattering across the pitch-angle, θ, of 90• , particles are isotropized in the backward hemisphere (relative to the outflow velocity vector) and self-generated waves have a steep, ∝k −3 wavenumber spectrum; (ii) if background waves have large intensities, enabling particles to cross θ = 90• , particles can be fully isotropized. In case (i), however, the calculated self-generated wave amplitudes are close to the magnitude of the ordered field for reasonable choices of model parameters, giving the particles a chance to be scattered across the resonance gap by non-resonant processes. If the resonance gap is filled, a large fraction of the pick-up particles is expected to return to the upstream region, and an ultra-relativistic shock wave is predicted to form in front of the outflow, where the two relativistic particle populations (ambient and reflected) mix and form a relativistic plasma. Reflection of pick-up protons decreases the π 0 -decay luminosity of relativistic outflows, leading to a need to update parameters of previous modeling. An example of outflow parameters reproducing typical TeV-blazar observations is presented.

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Proton transport through self-generated waves in impulsive flares

Cited by 9 publications

References 19 publications

On the generation of Alfvén waves by solar energetic particles

On the generation of Alfvén waves by solar energetic particles

Current views on impulsive and gradual solar energetic particle events

Conversion of bulk kinetic energy into radiation in AGNs and GRBs: Particle transport effects

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