Energetic Nonthermal Electrons within the Above-the-looptop Regions in Solar Flares: Acceleration, Feedback, and Quasiperiodic Pulsations

Journal Article · Thu Jan 29 00:00:00 EST 2026 · The Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/ae2de6· OSTI ID:3017775

Seo, Jeongbhin ^[1]; Guo, Fan ^[2]; Li, Xiaocan ^[1]; Chen, Bin ^[3]; Shen, Chengcai ^[4]; Li, Hui ^[1]

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1. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States)
3. New Jersey Institute of Technology (NJIT), Newark, NJ (United States)
4. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA (United States)

Solar flares are among the most dramatic events in the solar system, releasing substantial magnetic energy and accelerating a large number of electrons to high energies. Notably, in certain events, the above-the-looptop region may contain a significant population of nonthermal electrons, both in number and energy. For the first time, we adopt a novel numerical method that combines magnetohydrodynamics with energetic particles incorporating feedback from nonthermal electrons to investigate electron acceleration and transport in solar flares. We find that a large fraction of energetic electrons are accelerated via the current sheet and termination shock regions. Most energetic electrons are concentrated in the above-the-looptop region, carrying a sizable amount of the released energy. We observe that greater feedback of nonthermal electrons leads to steeper energy spectra. The energy density of the nonthermal electrons oscillates due to the periodic impact of magnetic islands into the above-the-looptop region, which may help explain the observed quasiperiodic pulsations. Our simulations provide new insights into the origin of nonthermal electrons and associated emissions in the above-the-looptop region.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); National Energy Research Scientific Computing Center (NERSC); National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)
• Grant/Contract Number: 89233218CNA000001
• Other Award/Contract Number: C5509; 20240477CR; 2334932; AGS-2334930; AST-2107745; AST-2108853; NNH17AE68I; 80HQTR20T0073; 80HQTR21T0005; 80HQTR21T0117; NNH230B17A; NNH240B72A; FES-ERCAP0031616
• OSTI ID: 3017775
• Report Number(s): LA-UR--25-30420; 10.3847/1538-4357/ae2de6; 1538-4357
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 2 Vol. 997; ISSN 0004-637X; ISSN 1538-4357
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS