Hard X-ray emitting energetic electrons and photospheric electric currents

Musset, Sophie; Vilmer, Nicole; Bommier, V.

doi:10.1051/0004-6361/201424378

Cited by 29 publications

(27 citation statements)

References 45 publications

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“…The upward current contours clearly coincide with the higher intensity. This is confirmed by the more energetic emissions at 94 Å shown in Figure5 of Musset et al (2015). Indeed, there is no overlap between the brightness contours in this figure with that of the downward current region shown in Figure 1 (bottom of the same paper) but rather a striking coincidence with those of the upward current.…”

Section: The Evidencesupporting

confidence: 72%

“…Indeed, there is no overlap between the brightness contours in this figure with that of the downward current region shown in Figure 1 (bottom of the same paper) but rather a striking coincidence with those of the upward current. Also the hard X-ray contours from RHESSI, analyzed by the latter authors, exhibit a preferred coincidence of the maxima with the upward current ribbons (compare with the remark in Section 4.2 of Musset et al 2015). It must be noted, however, that there is no one-to-one correspondence between the upward current and high intensity.…”

Section: The Evidencementioning

confidence: 71%

“…By contrast, the determination of the 3D photospheric field and current density suffers from the limited spatial resolution of about 1 5. I therefore assume that the magnetic perturbation field due to the upward current amounted to about 10% of the vertical field of up to about 2000 G (Janvier et al 2014;Musset et al 2015). This corresponds to a considerable shear field.…”

Section: Consequencesmentioning

confidence: 99%

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Evidence for Field-parallel Electron Acceleration in Solar Flares

Haerendel

2017

ApJ

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It is proposed that the coincidence of higher brightness and upward electric current observed by Janvier et al. during a flare indicates electron acceleration by field-parallel potential drops sustained by extremely strong fieldaligned currents of the order of 10 4 A m −2 . A consequence of this is the concentration of the currents in sheets with widths of the order of 1 m. The high current density suggests that the field-parallel potential drops are maintained by current-driven anomalous resistivity. The origin of these currents remains a strong challenge for theorists.

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Section: The Evidencesupporting

confidence: 72%

Section: The Evidencementioning

confidence: 71%

Section: Consequencesmentioning

confidence: 99%

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Evidence for Field-parallel Electron Acceleration in Solar Flares

Haerendel

2017

ApJ

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“…In the February 2011 flare, the electric current density also increases in some regions of the current ribbons, namely near the straight part and at the tip of the hook of the J-shaped ribbon and the current ribbons display a very clear J shape. The locations of current increase were also associated with strong hard X-ray emissions (Musset et al 2015). …”

Section: Electric Current Increase In the Impulsive Phasementioning

confidence: 99%

Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

Janvier

Savcheva

Pariat

et al. 2016

A&A

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Context. The standard model for eruptive flares has been extended to three dimensions (3D) in the past few years. This model predicts typical J-shaped photospheric footprints of the coronal current layer, forming at similar locations as the quasi-separatrix layers (QSLs). Such a morphology is also found for flare ribbons observed in the extreme ultraviolet (EUV) band, and in nonlinear force-free field (NLFFF) magnetic field extrapolations and models. Aims. We study the evolution of the photospheric traces of the current density and flare ribbons, both obtained with the Solar Dynamics Observatory instruments. We aim to compare their morphology and their time evolution, before and during the flare, with the topological features found in a NLFFF model. Methods. We investigated the photospheric current evolution during the 06 September 2011 X-class flare (SOL2011-09-06T22:20) occurring in NOAA AR 11283 from observational data of the magnetic field obtained with the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory. We compared this evolution with that of the flare ribbons observed in the EUV filters of the Atmospheric Imager Assembly. We also compared the observed electric current density and the flare ribbon morphology with that of the QSLs computed from the flux rope insertion method-NLFFF model.Results. The NLFFF model shows the presence of a fan-spine configuration of overlying field lines, due to the presence of a parasitic polarity, embedding an elongated flux rope that appears in the observations as two parts of a filament. The QSL signatures of the fan configuration appear as a circular flare ribbon that encircles the J-shaped ribbons related to the filament ejection. The QSLs, evolved via a magnetofrictional method, also show similar morphology and evolution as both the current ribbons and the EUV flare ribbons obtained several times during the flare. Conclusions. For the first time, we propose a combined analysis of the photospheric traces of an eruptive flare, in a complex topology, with direct measurements of electric currents and QSLs from observational data and a magnetic field model. The results, obtained by two different and independent approaches 1) confirm previous results of current increase during the impulsive phase of the flare and 2) show how NLFFF models can capture the essential physical signatures of flares even in a complex magnetic field topology.

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“…For a rapid release, the currents must be concentrated into small regions (e.g., Priest and Forbes 2000). Such currents may be inferred observationally in regions with a tangential discontinuity of the magnetic field direction in the system of rising loops near the base of the corona (Solanki et al 2003;Musset et al 2015).…”

Section: Flares and Photospheric Field Configurationmentioning

confidence: 99%

Flare Observations

Benz

2016

Living Rev Sol Phys

497

317

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Solar flares are observed at all wavelengths from decameter radio waves to gamma-rays beyond 1 GeV. This review focuses on recent observations in EUV, soft and hard X-rays, white light, and radio waves. Space missions such as RHESSI, Yohkoh, TRACE, SOHO, and more recently Hinode and SDO have enlarged widely the observational base. They have revealed a number of surprises: Coronal sources appear before the hard X-ray emission in chromospheric footpoints, major flare acceleration sites appear to be independent of coronal mass ejections, electrons, and ions may be accelerated at different sites, there are at least 3 different magnetic topologies, and basic characteristics vary from small to large flares. Recent progress also includes improved insights into the flare energy partition, on the location(s) of energy release, tests of energy release scenarios and particle acceleration. The interplay of observations with theory is important to deduce the geometry and to disentangle the various processes involved. There is increasing evidence supporting magnetic reconThis article is a revised version of https://doi.org/10.12942/lrsp-2008-1. Change summary Major revision, updated and expanded. Change details Significant new results from RHESSI and SDO are included. In particular, Sect. 3.4 on "Emissions from above the coronal source" was added (including two new figures) and Sect. 3.2 on "Coronal hard X-ray sources" was expanded. New observations of flares in white light are reported (replaced Fig. 25 with a movie), as well as recent multi-wavelength observations in radio waves and gamma-rays combined with hard X-rays. Four references were removed and 49 new references added. Arnold O. Benz nection as the basic cause. While this process has become generally accepted as the trigger, it is still controversial how it converts a considerable fraction of the energy into non-thermal particles. Flare-like processes may be responsible for large-scale restructuring of the magnetic field in the corona as well as for its heating. Large flares influence interplanetary space and substantially affect the Earth's ionosphere. Flare scenarios have slowly converged over the past decades, but every new observation still reveals major unexpected results, demonstrating that solar flares, after 150 years since their discovery, remain a complex problem of astrophysics including major unsolved questions. Electronic supplementary material

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Hard X-ray emitting energetic electrons and photospheric electric currents

Cited by 29 publications

References 45 publications

Evidence for Field-parallel Electron Acceleration in Solar Flares

Evidence for Field-parallel Electron Acceleration in Solar Flares

Evolution of flare ribbons, electric currents, and quasi-separatrix layers during an X-class flare

Flare Observations

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