The efficiency of electron acceleration during the impulsive phase of a solar flare
arXiv:2304.01088 · doi:10.3847/2041-8213/acc9b7
Abstract
Solar flares are known to be prolific electron accelerators, yet identifying the mechanism(s) for such efficient electron acceleration in solar flare (and similar astrophysical settings) presents a major challenge. This is due in part to a lack of observational constraints related to conditions in the primary acceleration region itself. Accelerated electrons with energies above 20~keV are revealed by hard X-ray (HXR) bremsstrahlung emission, while accelerated electrons with even higher energies manifest themselves through radio gyrosynchrotron emission. Here we show, for a well-observed flare on 2017~September~10, that a combination of \emph{RHESSI} hard X-ray and and SDO/AIA EUV observations provides a robust estimate of the fraction of the ambient electron population that is accelerated at a given time, with an upper limit of on the number density of nonthermal (~keV) electrons, expressed as a fraction of the number density of ambient protons in the same volume. This upper limit is about two orders of magnitude lower than previously inferred from microwave observations of the same event. Our results strongly indicate that the fraction of accelerated electrons in the coronal region at any given time is relatively small, but also that the overall duration of the HXR emission requires a steady resupply of electrons to the acceleration site. Simultaneous measurements of the instantaneous accelerated electron number density and the associated specific electron acceleration rate provide key constraints for a quantitative study of the mechanisms leading to electron acceleration in magnetic reconnection events.
5 figures, 10 pages
References in corpus (14)
- Measurement of magnetic field and relativistic electrons along a solar flare current sheet
- Global Energetics of Solar Flares: V. Energy Closure in Flares and Coronal Mass Ejections
- Double Coronal Hard and Soft X-ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares
- Electron Acceleration during Macroscale Magnetic Reconnection
- Relations between concurrent hard X-ray sources in solar flares
- Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop
- Kappa distribution and hard X-ray emission of solar flares
- On the variation of solar flare coronal x-ray source sizes with energy
- Energetic Electron Distribution of the Coronal Acceleration Region: First results from Joint Microwave and Hard X-ray Imaging Spectroscopy
- Onset of turbulent fast magnetic reconnection observed in the solar atmosphere
- Understanding breaks in solar flares x-ray spectra: Evaluation of a co-spatial return-current model
- Determination of the total accelerated electron rate and power using solar flare hard X-ray spectra
- Electron distribution and energy release in magnetic reconnection outflow regions during the pre-impulsive phase of a solar flare
- Spectral and Imaging Diagnostics of Spatially-Extended Turbulent Electron Acceleration and Transport in Solar Flares