The Efficiency of Electron Acceleration during the Impulsive Phase of a Solar Flare

0571482 - ASÚ 2024 RIV US eng J - Journal Article
Kontar, E. P. - Emslie, A.G. - Motorina, Galina - Dennis, B. R.
The Efficiency of Electron Acceleration during the Impulsive Phase of a Solar Flare.
Astrophysical Journal Letters. Roč. 947, č. 1 (2023), č. článku L13. ISSN 2041-8205. E-ISSN 2041-8213
R&D Projects: GA ČR(CZ) GC21-16508J; GA MŠMT(CZ) LM2018106
Institutional support: RVO:67985815
Keywords : solar flares * solar physics * solar activity
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 7.9, year: 2022
Method of publishing: Open access

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 similar to 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 RHESSI HXR and and the Solar Dynamics Observatory/Atmospheric Imaging Assembly (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 less than or similar to 10(-2) on the number density of nonthermal (>= 20 keV) electrons, expressed as a fraction of the number density of ambient protons in the same volume. This upper limit is about 2 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.
Permanent Link: https://hdl.handle.net/11104/0343109