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The efficiency of electron acceleration during the impulsive phase of a solar flare View all abstracts by submitter

Eduard Kontar   Submitted: 2023-04-04 06:17

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 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 ≈ 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 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.

Authors: Eduard P. Kontar, A. Gordon Emslie, Galina G. Motorina, Brian R. Dennis
Projects: Owens Valley Solar Array,RHESSI

Publication Status: submitted to ApJ Letters
Last Modified: 2023-04-05 05:20
Go to main E-Print page  The Evolution of Plasma Composition During a Solar Flare  Evolution of Solar Eruptive Events: Investigating the Relationships Among Magnetic Reconnection, Flare Energy Release, and Coronal Mass Ejections  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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