Acceleration, Magnetic Fluctuations, and Cross-Field Transport of Energetic Electrons in a Solar Flare Loop

Kontar, Eduard P.; Hannah, I. G.; Bian, N. H.

doi:10.1088/2041-8205/730/2/l22

Cited by 56 publications

(96 citation statements)

References 48 publications

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“…These values are in good agreement with what has been found for a few events by Kontar et al (2011) and Guo et al (2012). In their work, Xu et al (2008) modelled the transport of electrons on the basis of a standard collisional transport model.…”

Section: −Febsupporting

confidence: 86%

Hard X-ray emitting energetic electrons and photospheric electric currents

Musset

Vilmer

Bommier

2015

A&A

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Context. The energy released during solar flares is believed to be stored in non-potential magnetic fields associated with electric currents flowing in the corona. While no measurements of coronal electric currents are presently available, maps of photospheric electric currents can now be derived from SDO/HMI observations. Photospheric electric currents have been shown to be the tracers of the coronal electric currents. Particle acceleration can result from electric fields associated with coronal electric currents. We revisit here some aspects of the relationship between particle acceleration in solar flares and electric currents in the active region. Aims. We study the relation between the energetic electron interaction sites in the solar atmosphere, and the magnitudes and changes of vertical electric current densities measured at the photospheric level, during the X2.2 flare on February 15, 2011, in AR NOAA 11158. Methods. X-ray images from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) are overlaid on magnetic field and electric current density maps calculated from the spectropolarimetric measurements of the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) using the UNNOFIT inversion and Metcalf disambiguation codes. X-ray images are also compared with extreme ultraviolet (EUV) images from the SDO Atmospheric Imaging Assembly (AIA) to complement the flare analysis. Results. Part of the elongated X-ray emissions from both thermal and non-thermal electrons overlay the elongated narrow current ribbons observed at the photospheric level. A new X-ray source at 50−100 keV (produced by non-thermal electrons) is observed in the course of the flare and is cospatial with a region in which new vertical photospheric currents appeared during the same period (an increase of 15%). These observational results are discussed in the context of the scenarios in which magnetic reconnection (and subsequent plasma heating and particle acceleration) occurs at current-carrying layers in the corona.

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Section: −Febsupporting

confidence: 86%

Hard X-ray emitting energetic electrons and photospheric electric currents

Musset

Vilmer

Bommier

2015

A&A

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“…However, the displacements we found between the metric sources and the flaring loops appear too large (55−300 ) to be interpreted in terms of cross-field transport of the energetic electrons. For example, Kontar et al (2011) found that the cross-field transport of electrons with energies 8−25 keV in a flaring loop yielded excursions that were not larger than 1−2 .…”

Section: Discussionmentioning

confidence: 99%

A tiny event producing an interplanetary type III burst

Alissandrakis

Nindos

Patsourakos

et al. 2015

A&A

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Aims. We investigate the conditions under which small-scale energy release events in the low corona gave rise to strong interplanetary (IP) type III bursts. Methods. We analyzed observations of three tiny events, detected by the Nançay Radio Heliograph (NRH), two of which produced IP type III bursts. We took advantage of the NRH positioning information and of the high cadence of AIA/SDO data to identify the associated extreme-UV (EUV) emissions. We measured positions and time profiles of the metric and EUV sources. Results. We found that the EUV events that produced IP type III bursts were located near a coronal hole boundary, while the one that did not was located in a closed magnetic field region. In all three cases tiny flaring loops were involved, without any associated mass eruption. In the best observed case, the radio emission at the highest frequency (435 MHz) was displaced by ∼55 with respect to the small flaring loop. The metric type III emission shows a complex structure in space and in time, indicative of multiple electron beams, despite the low intensity of the events. From the combined analysis of dynamic spectra and NRH images, we derived the electron beam velocity as well as the height, ambient plasma temperature, and density at the level of formation of the 160 MHz emission. From the analysis of the differential emission measure derived from the AIA images, we found that the first evidence of energy release was at the footpoints, and this was followed by the development of flaring loops and subsequent cooling. Conclusions. Even small energy release events can accelerate enough electrons to give rise to powerful IP type III bursts. The proximity of the electron acceleration site to open magnetic field lines facilitates the escape of the electrons into the interplanetary space. The offset between the site of energy release and the metric type III location warrants further investigation.

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“…also demonstrated that reconnection in twisted loops with magnetic field convergence near footpoints could provide a configuration for particle re-acceleration in the lower corona and chromosphere (Brown et al 2009). They also show that the developed model can explain some features of the variation in hard X-ray sources recently observed with RHESSI (Kontar et al 2011). used the model developed in Hood et al (2009) and to study particle acceleration in twisted loops using the test-particle approach.…”

Section: Introductionmentioning

confidence: 91%

Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere

Gordovskyy

Browning

Kontar

et al. 2014

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Context. Twisted coronal loops should be ubiquitous in the solar corona. Twisted magnetic fields contain excess magnetic energy, which can be released during magnetic reconnection, causing solar flares. Aims. The aim of this work is to investigate magnetic reconnection, and particle acceleration and transport in kink-unstable twisted coronal loops, with a focus on the effects of resistivity, loop geometry and atmospheric stratification. Another aim is to perform forward-modelling of bremsstrahlung emission and determine the structure of hard X-ray sources. Methods. We use a combination of magnetohydrodynamic (MHD) and test-particle methods. First, the evolution of the kinking coronal loop is considered using resistive MHD model, incorporating atmospheric stratification and loop curvature. Then, the obtained electric and magnetic fields and density distributions are used to calculate electron and proton trajectories using a guiding-centre approximation, taking into account Coulomb collisions. Results. It is shown that electric fields in twisted coronal loops can effectively accelerate protons and electrons to energies up to 10 MeV. High-energy particles have hard, nearly power-law energy spectra. The volume occupied by high-energy particles demonstrates radial expansion, which results in the expansion of the visible hard X-ray loop and a gradual increase in hard X-ray footpoint area. Synthesised hard X-ray emission reveals strong footpoint sources and the extended coronal source, whose intensity strongly depends on the coronal loop density.

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Acceleration, Magnetic Fluctuations, and Cross-Field Transport of Energetic Electrons in a Solar Flare Loop

Cited by 56 publications

References 48 publications

Hard X-ray emitting energetic electrons and photospheric electric currents

Hard X-ray emitting energetic electrons and photospheric electric currents

A tiny event producing an interplanetary type III burst

Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere

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