A Magnetic Reconnection Mechanism for the Generation of Anomalous Cosmic Rays

Drake, J. F.; Opher, M.; Swisdak, M.; Chamoun, J. N.

doi:10.1088/0004-637x/709/2/963

Cited by 278 publications

(337 citation statements)

References 54 publications

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“…The electrons gain energy by bouncing back and forth within the reconnection layer. Upon each cycle, the energy gain is ∆γ ∼ γ, which demonstrates that the acceleration mechanism is a first-order Fermi process [11,30]. To show this more rigorously, we have tracked the energy change of all the particles in the simulation and contributions from the parallel electric field (m e c 2 ∆γ = qv E dt) and curvature drift acceleration (m e c 2 ∆γ = qv curv · E ⊥ dt) similar to [31], where…”

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confidence: 94%

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

et al. 2014

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Using fully kinetic simulations, we demonstrate that magnetic reconnection in relativistic plasmas is highly efficient at accelerating particles through a first-order Fermi process resulting from the curvature drift of particles in the direction of the electric field induced by the relativistic flows. This mechanism gives rise to the formation of hard power-law spectra in parameter regimes where the energy density in the reconnecting field exceeds the rest mass energy density σ ≡ B 2 /(4πnmec 2 ) > 1 and when the system size is sufficiently large. In the limit σ 1, the spectral index approaches p = 1 and most of the available energy is converted into non-thermal particles. A simple analytic model is proposed which explains these key features and predicts a general condition under which hard power-law spectra will be generated from magnetic reconnection.PACS numbers: 52.27. Ny, 52.35.Vd, 98.54.Cm, 98.70.Rz Introduction -Magnetic reconnection is a fundamental plasma process that allows rapid changes of magnetic field topology and the conversion of magnetic energy into plasma kinetic energy. It has been extensively discussed in solar flares, Earth's magnetosphere, and laboratory applications. However, magnetic reconnection remains poorly understood in high-energy astrophysical systems [1]. Magnetic reconnection has been suggested as a mechanism for producing high-energy emissions from pulsar wind nebula, gamma-ray bursts, and jets from active galactic nuclei [2][3][4][5][6]. In those systems, it is often expected that the magnetization parameter σ ≡ B 2 /(4πnmc 2 ) exceeds unity. Most previous kinetic studies focused on the non-relativistic regime σ < 1 and reported several acceleration mechanisms such as acceleration at X-line regions [7][8][9] and Fermi-type acceleration within magnetic islands [8][9][10][11]. More recently, the regime σ = 1-100 has been explored using pressure-balanced current sheets and strong particle acceleration has been found in both diffusion regions [12][13][14][15] and island regions [16,17]. However, this initial condition requires a hot plasma component inside the current sheet to maintain force balance, which may not be justified for high-σ plasmas.

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confidence: 94%

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

et al. 2014

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“…It can be efficient in collisionless plasmas (Drake et al 2006(Drake et al , 2010Bessho & Bhattacharjee 2012) or in collisional plasmas (Kowal et al 2011) where reconnection is fast because of turbulence. For a closer analysis, the ratio of Larmor radii to typical sizes of the magnetic islands is key.…”

Section: Introductionmentioning

confidence: 99%

“…But to what extent this kinetic energy is distributed between the bulk flow velocity of the outflows, their thermal energy, and a possible high-energy tail, as well as the properties of the high-energy tail, are open questions. This mechanism is inefficient for non-relativistic reconnection because the acceleration zone is too short (along the outflow direction) (Drake et al 2010;Kowal et al 2011;Drury 2012) and affects too few particles, but is efficient under relativistic conditions where the larger reconnection electric field creates a wider acceleration zone (Zenitani & Hoshino 2001. It has indeed been found, with PIC simulations of relativistic reconnection, that power-law tails are produced through particle acceleration by E rec .…”

Section: Introductionmentioning

confidence: 99%

The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

Melzani

Walder

Folini

et al. 2014

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Collisionless magnetic reconnection is a prime candidate to account for flare-like or steady emission, outflow launching, or plasma heating, in a variety of high-energy astrophysical objects, including ones with relativistic ion-electron plasmas. But the fate of the initial magnetic energy in a reconnection event remains poorly known. What are the amounts assigned to kinetic energy, the ion and electron distribution, and the hardness of the particle distributions? We explored these questions with 2D particle-in-cell simulations of ion-electron plasmas. We find that 45 to 75% of the total initial magnetic energy ends up in kinetic energy, this fraction increasing with the inflow magnetization. Depending on the guide field strength, ions get from 30% to 60% of the total kinetic energy. Particles can be separated into two populations that mix only weakly: (i) particles initially in the current sheet heated by its initial tearing and subsequent contraction of the islands, and (ii) particles from the background plasma that primarily gain energy via the reconnection electric field when passing near the X-point. Particles of (ii) tend to form a power law with an index p = −dlog n(γ)/dlog γ that depends mostly on the inflow Alfvén speed V A and magnetization σ s of species s. For electrons p = 5 to 1.2 for increasing σ e . The highest particle Lorentz factor for ions or electrons increases roughly linearly with time for all the relativistic simulations. This is faster, and the spectra can be harder, than for collisionless shock acceleration. We discuss applications to microquasar and AGN coronae, to extragalactic jets, and to radio lobes. We point out situations where effects, such as Compton drag or pair creation, are important.

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“…Mason et al, 1986;Reames, Meyer, and von Rosenvinge, 1994; Article 2) suggests the operation of two physical mechanisms. Recently, the heavy-element enhancements, relative to coronal abundances, and their strong power-law dependence on A/Q of the ions in impulsive SEP events, have been linked theoretically to the physics of magneticreconnection regions from which the ions escape (Drake et al, 2009(Drake et al, , 2010Knizhnik, Swizdak, and Drake 2011;Drake and Swizdak, 2014). This model is based upon particle-in-cell (PIC) calculations.…”

Section: Introductionmentioning

confidence: 99%

Temperature of the Source Plasma for Impulsive Solar Energetic Particles

2015

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The steep power-law dependence of element abundance enhancements on the mass-tocharge ratios [A/Q] of the ions in impulsive solar energetic-particle (SEP) events causes these enhancements to reflect the temperature-dependent pattern of Q of the ions in the source plasma.We searched for SEP events from coronal plasma that is hotter or cooler than the limited region of 2.5 -3.2 MK previously found to dominate 111 impulsive SEP events. Fifteen new events were found, four (three) originated in 2-MK (4-MK) plasma, but none from outside this temperature range. Although the impulsive SEP events are strongly associated with flares, this result indicates that these ions are not accelerated from flare-heated plasma, which can often exceed 10 MK.Evidently the ions of 2 -20 MeV amu -1 that we observe in space are accelerated from activeregion plasma on open magnetic-field lines near the flare, but not from the closed loops of the flare. The power-law dependence of the abundance enhancements on A/Q of the ions is expected from theoretical models of acceleration from regions of magnetic reconnection.

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A Magnetic Reconnection Mechanism for the Generation of Anomalous Cosmic Rays

Cited by 278 publications

References 54 publications

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

Formation of Hard Power Laws in the Energetic Particle Spectra Resulting from Relativistic Magnetic Reconnection

The energetics of relativistic magnetic reconnection: ion-electron repartition and particle distribution hardness

Temperature of the Source Plasma for Impulsive Solar Energetic Particles

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