Electron distribution and energy release in magnetic reconnection outflow regions during the pre-impulsive phase of a solar flare

Abstract

We present observations of electron energization in magnetic reconnection outflows during the pre-impulsive phase of solar flare SOL2012-07-19T05:58. During a time-interval of about 20 minutes, starting 40 minutes before the onset of the impulsive phase, two X-ray sources were observed in the corona, one above the presumed reconnection region and one below. For both of these sources, the mean electron distribution function as a function of time is determined over an energy range from 0.1~keV up to several tens of keV, for the first time. This is done by simultaneous forward fitting of X-ray and EUV data. Imaging spectroscopy with RHESSI provides information on the high-energy tail of the electron distribution in these sources while EUV images from SDO/AIA are used to constrain the low specific electron energies. The measured electron distribution spectrum in the magnetic reconnection outflows is consistent with a time-evolving kappa-distribution with $\kappa =3.5-5.5$. The spectral evolution suggests that electrons are accelerated to progressively higher energies in the source above the reconnection region, while in the source below, the spectral shape does not change but an overall increase of the emission measure is observed, suggesting density increase due to evaporation. The main mechanisms by which energy is transported away from the source regions are conduction and free-streaming electrons. The latter dominates by more than one order of magnitude and is comparable to typical non-thermal energies during the hard X-ray peak of solar flares, suggesting efficient acceleration even during this early phase of the event.

arXiv comment9 pages, 5 figures, accepted for publication in ApJ

References in corpus (25)

• Global Energetics of Thirty-Eight Large Solar Eruptive Events
• Implications of X-ray Observations for Electron Acceleration and Propagation in Solar Flares
• Direct Evidence for a Fast CME Driven by the Prior Formation and Subsequent Destabilization of a Magnetic Flux Rope
• Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows
• Deducing Electron Properties From Hard X-Ray Observations
• Relations between concurrent hard X-ray sources in solar flares
• Kappa Distribution Model for Hard X-Ray Coronal Sources of Solar Flares
• Turbulent kinetic energy in the energy balance of a solar flare
• Observations of conduction driven evaporation in the early rise phase of solar flares
• Global Energetics of Solar Flares: III. Non thermal Energies
• Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares
• Kappa distribution and hard X-ray emission of solar flares
• Collisional relaxation of electrons in a warm plasma and accelerated nonthermal electron spectra in solar flares
• Magnetic Reconnection Null Points as the Origin of Semi-relativistic Electron Beams in a Solar Jet
• Properties of the Acceleration Regions in Several Loop-structured Solar Flares
• Acceleration, magnetic fluctuations and cross-field transport of energetic electrons in a solar flare loop
• On the variation of solar flare coronal x-ray source sizes with energy
• Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles
• Differential emission measure Analysis of a limb solar flare on 2012 July 19
• Multi-thermal representation of the kappa-distribution of solar flare electrons and application to simultaneous X-ray and EUV observations
• Electron Distribution Functions in Solar Flares from combined X-ray and EUV Observations
• Thermal to Nonthermal Energy Partition at the Early Rise Phase of Solar Flares
• Microwave imaging of a hot flux rope structure during the pre-impulsive stage of an eruptive M7.7 solar flare
• Where is the chromospheric response to conductive energy input from a hot pre-flare coronal loop?
• Differential Emission Measure and Electron Distribution Function Reconstructed from RHESSI and SDO Observations

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