Particle acceleration in reconnecting current sheets

Litvinenko, Yu. E.; Сомов, Б. В.

doi:10.1007/bf00662174

Cited by 121 publications

(119 citation statements)

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“…The mechanism that releases magnetic energy is known as magnetic reconnection. Observational as well as theoretical aspects of this mechanism have been studied in detail (e.g., Parker 1963;Demoulin et al 1993;Litvinenko & Somov 1993;Yokoyama et al 2001;Aulanier et al 2006;Veronig et al 2006;Su et al 2013;Dudík et al 2014;van Driel-Gesztelyi et al 2014;Li & Zhang 2015).…”

Section: Introductionmentioning

confidence: 99%

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Gömöry

Veronig

et al. 2016

A&A

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Aims. We study the response of the solar atmosphere during a GOES M1.6 flare using spectroscopic and imaging observations. In particular, we examine the evolution of the mass flows and electron density together with the energy input derived from hard X-ray (HXR) in the context of chromospheric evaporation.Methods. We analyzed high-cadence sit-and-stare observations acquired with the Hinode/EIS spectrometer in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T = 6.4) spectral lines to derive temporal variations of the line intensity, Doppler shifts, and electron density during the flare. We combined these data with HXR measurements acquired with RHESSI to derive the energy input to the lower atmosphere by flare-accelerated electrons.Results. During the flare impulsive phase, we observe no significant flows in the cooler Fe xiii line but strong upflows, up to 80-150 km s −1 , in the hotter Fe xvi line. The largest Doppler shifts observed in the Fe xvi line were co-temporal with the sharp intensity peak. The electron density obtained from a Fe xiii line pair ratio exhibited fast increase (within two minutes) from the pre-flare level of 5.01 × 10 9 cm −3 to 3.16 × 10 10 cm −3 during the flare peak. The nonthermal energy flux density deposited from the coronal acceleration site to the lower atmospheric layers during the flare peak was found to be 1.34 × 10 10 erg s −1 cm −2 for a low-energy cut-off that was estimated to be 16 keV. During the decline flare phase, we found a secondary intensity and density peak of lower amplitude that was preceded by upflows of ∼15 km s −1 that were detected in both lines. The flare was also accompanied by a filament eruption that was partly captured by the EIS observations. We derived Doppler velocities of 250-300 km s −1 for the upflowing filament material. Conclusions. The spectroscopic results for the flare peak are consistent with the scenario of explosive chromospheric evaporation, although a comparatively low value of the nonthermal energy flux density was determined for this phase of the flare. This outcome is discussed in the context of recent hydrodynamic simulations. It provides observational evidence that the response of the atmospheric plasma strongly depends on the properties of the electron beams responsible for the heating, in particular the steepness of the energy distribution. The secondary peak of line intensity and electron density detected during the decline phase is interpreted as a signature of flare loops being filled by expanding hot material that is due to chromospheric evaporation.

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Section: Introductionmentioning

confidence: 99%

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Gömöry

Veronig

et al. 2016

A&A

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“…A number of authors (e.g. Martens & Young 1990;Litvinenko & Somov 1993;Litvinenko 1996) analytically studied particle acceleration by the electric field in CS and estimated energies gained by adiabatic and non-adiabatic particles. However, the analytical approach is limited to simple electric and magnetic field configurations, while numerical simulations are needed for more complex cases.…”

Section: Introductionmentioning

confidence: 99%

Particle acceleration in a transient magnetic reconnection event

Gordovskyy¹,

Browning²,

Vekstein³

2010

A&A

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Context. In the present paper, we investigate particle acceleration by direct electric field in solar flares. Aims. Proton and electron kinetics are considered based on MHD simulations of magnetic reconnection, with the aim of determining the properties of accelerated particles in a time-dependent reconnecting event model. Methods. At first, we considered several two-dimensional numerical models of forced reconnection in the initially force-free Harris current sheet. The electric and magnetic fields from these models were then used to study proton and electron motion with the guiding centre, test particle approach. Results. It is shown that protons and electrons can be accelerated to very high energies up to tens of MeV in the present model. The energy spectra for both particle species are combinations of exponential and rather hard power-law shapes. Also, protons and electrons are ejected from the CS in different directions.

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“…Further evolution of the electron beam during its steady precipitation into deeper atmospheric levels is described by the time-dependent Fokker-Planck equation (Paper I). We assume that ambient electrons are dragged into a reconnecting current sheet (RCS) formed by interacting magnetic loops and then steadily accelerated by a super-Dreicer electric field in the sheet (e.g., Litvinenko & Somov 1993;Zharkova & Agapitov 2009;Siversky & Zharkova 2009b). Such a process results in a steady ejection of electrons with power-law energy distribution from the current sheet into the loop.…”

Section: Simulation Modelmentioning

confidence: 99%

Manifestations of Energetic Electrons With Anisotropic Distributions in Solar Flares. Ii. Gyrosynchrotron Microwave Emission

Kuznetsov¹,

Zharkova²

2010

ApJ

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We investigate the spectra and polarization of the gyrosynchrotron microwave (MW) emission generated by anisotropic electron beams in the solar corona. The electron distributions are selected from the steady propagation/ precipitation model of beam electrons obtained from the time-dependent solutions of the Fokker-Planck equation taking into account particle anisotropic precipitation into a converging magnetic tube while losing energy in collisions and Ohmic losses induced by a self-induced electric field. We separate the effects of converging magnetic field from those of self-induced electric field for beams with different initial energy fluxes and spectral indices. The effect of returning electrons of the beam is negligible for the beams with relatively weak energy fluxes (F 10 10 erg cm −2 s −1 ), while it becomes very important for the electron beams with F 10 12 erg cm −2 s −1 . Electric field-induced losses lead to the increase of MW emission intensity, especially at larger viewing angles (θ 140 • , looking at the loop from a side). The polarization remains typical for the beam-like distributions. The combined effect of the self-induced electric field and converging magnetic field reveals a noticeable (up to a factor of 10) increase of the emission intensity (for the viewing angles θ 140 • -150 • ) in comparison with the models considering only collision factor, especially in the deeper precipitation layers (near the loop footpoints). Thus, considering the self-induced electric field is especially important for the resulting MW emission intensity, spectra shape, and polarization that can provide much closer correlation of simulations with observations in solar flares.

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Particle acceleration in reconnecting current sheets

Cited by 121 publications

References 7 publications

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Particle acceleration in a transient magnetic reconnection event

Manifestations of Energetic Electrons With Anisotropic Distributions in Solar Flares. Ii. Gyrosynchrotron Microwave Emission

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