Particle Acceleration in Fragmenting Periodic Reconnecting Current Sheets in Solar Flares

Gordovskyy, Mykola; Browning, Philippa; Vekstein, G.

doi:10.1088/0004-637x/720/2/1603

Cited by 65 publications

(50 citation statements)

References 31 publications

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“…We would possibly expect to findṄ LT /Ṅ FP ≤ 1 if the acceleration region is not near the looptop or even if the electrons are accelerated along the loop, due either to stochastic electric fields (e.g. Vlahos et al 2004;Turkmani et al 2006;Bian & Browning 2008;Gordovskyy et al 2010) or to re-acceleration by beam-generated Langmuir waves . We now discuss the result ofṄ LT /Ṅ FP > 1 in terms of magnetic trapping, injection properties, and pitch-angle scattering.…”

Section: Discussionmentioning

confidence: 99%

Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares

Simões¹,

Kontar²

2013

A&A

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The interrelation of hard X-ray (HXR) emitting sources and the underlying physics of electron acceleration and transport presents one of the major questions in high-energy solar flare physics. Spatially resolved observations of solar flares often demonstrate the presence of well-separated sources of bremsstrahlung emission, so-called coronal and footpoint sources. Using spatially resolved X-ray observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and recently improved imaging techniques, we investigate in detail the spatially resolved electron distributions in a few well-observed solar flares. The selected flares can be interpreted as having a standard geometry with chromospheric HXR footpoint sources related to thick-target X-ray emission and the coronal sources characterised by a combination of thermal and thin-target bremsstrahlung. Using imaging spectroscopy techniques, we deduce the characteristic electron rates and spectral indices required to explain the coronal and footpoint X-ray sources. We found that, during the impulsive phase, the electron rate at the looptop is several times (a factor of 1.7−8) higher than at the footpoints. The results suggest that a sufficient number of electrons accelerated in the looptop explain the precipitation into the footpoints and imply that electrons accumulate in the looptop. We discuss these results in terms of magnetic trapping, pitch-angle scattering, and injection properties. Our conclusion is that the accelerated electrons must be subject to magnetic trapping and/or pitch-angle scattering, keeping a fraction of the population trapped inside the coronal loops. These findings put strong constraints on the particle transport in the coronal source and provide quantitative limits on deka-keV electron trapping/scattering in the coronal source.

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Section: Discussionmentioning

confidence: 99%

Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares

Simões¹,

Kontar²

2013

A&A

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“…(1)−(4). A similar approach has been used by, for example Gordovskyy et al (2010b);Eradat Oskoui & Neukirch (2014). We also assume that the separation of spatial/temporal scales between the gyromotion and global field environment (mentioned in Sect.…”

Section: Relativistic Particle Dynamicsmentioning

confidence: 99%

Particle acceleration at a reconnecting magnetic separator

Threlfall

Neukirch

Parnell

et al. 2015

A&A

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Context. While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. Aims. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. Methods. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. Results. The effect upon particle behaviour of initial position, pitch angle, and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains several free parameters, and we study the effect of changing these parameters upon particle acceleration, in particular in view of the final particle energy ranges that agree with observed energy spectra.

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“…In this work, we treat electrons and ions as test particles embedded in a thermal (MHD) plasma. Particle acceleration associated with reconnection and shocks in magnetically dominated Newtonian plasmas in the solar corona is studied extensively with test particle approaches (Rosdahl & Galsgaard 2009, Gordovskyy et al 2010, Gordovskyy & Browning 2011a, Gordovskyy & Browning 2011b, Gordovskyy et al 2014, Zhou et al 2015, Pinto et al 2016, Zhou et al 2016, Ripperda et al 2017, Threlfall et al 2017 and even in relativistic plasmas in the context of pulsar wind nebulae (Porth et al 2016, Giacchè & Kirk 2017. The test particles are guided by MHD fields without giving feedback to these fields.…”

Section: Introductionmentioning

confidence: 99%

Reconnection and particle acceleration in interacting flux ropes – II. 3D effects on test particles in magnetically dominated plasmas

Ripperda

Porth

Xia

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We analyze particle acceleration in explosive reconnection events in magnetically dominated proton-electron plasmas. Reconnection is driven by large-scale magnetic stresses in interacting current-carrying flux tubes. Our model relies on development of currentdriven instabilities on macroscopic scales. These tilt-kink instabilities develop in an initially force-free equilibrium of repelling current channels. Using MHD methods we study a 3D model of repelling and interacting flux tubes in which we simultaneously evolve test particles, guided by electromagnetic fields obtained from MHD. We identify two stages of particle acceleration; Initially particles accelerate in the current channels, after which the flux ropes start tilting and kinking and particles accelerate due to reconnection processes in the plasma. The explosive stage of reconnection produces non-thermal energy distributions with slopes that depend on plasma resistivity and the initial particle velocity. We also discuss the influence of the length of the flux ropes on particle acceleration and energy distributions. This study extends previous 2.5D results to 3D setups, providing all ingredients needed to model realistic scenarios like solar flares, black hole flares and particle acceleration in pulsar wind nebulae: formation of strong resistive electric fields, explosive reconnection and non-thermal particle distributions. By assuming initial energy equipartition between electrons and protons, applying low resistivity in accordance with solar corona conditions and limiting the flux rope length to a fraction of a solar radius we obtain realistic energy distributions for solar flares with non-thermal power law tails and maximum electron energies up to 11 MeV and maximum proton energies up to 1 GeV.

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Particle Acceleration in Fragmenting Periodic Reconnecting Current Sheets in Solar Flares

Cited by 65 publications

References 31 publications

Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares

Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares

Particle acceleration at a reconnecting magnetic separator

Reconnection and particle acceleration in interacting flux ropes – II. 3D effects on test particles in magnetically dominated plasmas

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