2021/02/01 by Bin Chen, M. Battaglia, Marina Battaglia +3 · 2 citations
Biochemistry, Genetics and Molecular Biology · Medicine · Physics and Astronomy · #Acceleration #Astronomy #Atomic physics #Coronal plane #Electron #Geomagnetism and Paleomagnetism Studies #Ionosphere and magnetosphere dynamics #Materials science #Medicine #Microwave #Microwave imaging #Nuclear physics #Optics #Physics #Solar and Space Plasma Dynamics #Spectroscopy #X-ray #astro-ph.HE #astro-ph.SR
paper · pdf · doi:10.3847/2041-8213/abe471
12 pages, 5 figures, accepted for publication in The Astrophysical Journal Letters
openalex publication_date 2021/02/01 · arxiv created 2021/02/09 · openalex created_date 2021/02/15 · arxiv updated 2021/03/03 · openalex updated_date 2026/08/05
Abstract Nonthermal sources located above bright flare arcades, referred to as the “above-the-loop-top” sources, have been often suggested as the primary electron acceleration site in major solar flares. The X8.2 limb flare on 2017 September 10 features such an above-the-loop-top source, which was observed in both microwaves and hard X-rays (HXRs) by the Expanded Owens Valley Solar Array and the Reuven Ramaty High Energy Solar Spectroscopic Imager, respectively. By combining the microwave and HXR imaging spectroscopy observations with multifilter extreme ultraviolet and soft X-ray imaging data, we derive the coronal magnetic field and energetic electron distribution of the source over a broad energy range from <10 keV up to ∼MeV during the early impulsive phase of the flare. The source has a strong magnetic field of over 800 G. The best-fit electron distribution consists of a thermal “core” from ∼25 MK plasma. A nonthermal power-law “tail” joins the thermal core at ∼16 keV with a spectral index of ∼3.6, which breaks down at above ∼160 keV to >6.0. Temporally resolved analysis suggests that the electron distribution above the break energy rapidly hardens with the spectral index decreasing from >20 to ∼6.0 within 20 s, or less than ∼10 Alfvén crossing times in the source. These results provide strong support for the above-the-loop-top source as the primary site where an ongoing bulk acceleration of energetic electrons is taking place very early in the flare energy release.