The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar Flares

Xiangliang Kong, Fan Guo, Chengcai Shen, Bin Chen, Yao Chen, Sophie Musset, Lindsay Glesener, Peera Pongkitiwanichakul, Joe Giacalone

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Abstract

Nonthermal loop-top sources in solar flares are the most prominent observational signatures that suggest energy release and particle acceleration in the solar corona. Although several scenarios for particle acceleration have been proposed, the origin of the loop-top sources remains unclear. Here we present a model that combines a large-scale magnetohydrodynamic simulation of a two-ribbon flare with a particle acceleration and transport model for investigating electron acceleration by a fast-mode termination shock (TS) at the loop top. Our model provides spatially resolved electron distribution that evolves in response to the dynamic flare geometry. We find a concave-downward magnetic structure located below the flare TS, induced by the fast reconnection downflows. It acts as a magnetic trap to confine the electrons at the loop top for an extended period of time. The electrons are energized significantly as they cross the shock front, and eventually build up a power-law energy spectrum extending to hundreds of kiloelectron volts. We suggest that this particle acceleration and transport scenario driven by a flare TS is a viable interpretation for the observed nonthermal loop-top sources.

Original languageEnglish (US)
Article numberL37
JournalAstrophysical Journal Letters
Volume887
Issue number2
DOIs
StatePublished - Dec 20 2019

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Xiangliang Kong Fan Guo Chengcai Shen Bin Chen Yao Chen Sophie Musset Lindsay Glesener Peera Pongkitiwanichakul Joe Giacalone Xiangliang Kong Fan Guo Chengcai Shen Bin Chen Yao Chen Sophie Musset Lindsay Glesener Peera Pongkitiwanichakul Joe Giacalone Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, and Institute of Space Sciences, Shandong University, Weihai, Shandong 264209, People’s Republic of China State Key Laboratory of Space Weather, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China Los Alamos National Laboratory, Los Alamos, NM 87545, USA New Mexico Consortium, 4200 West Jemez Road, Los Alamos, NM 87544, USA Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA Center for Solar-Terrestrial Research, New Jersey Institute of Technology, 323 Dr. Martin Luther King Boulevard, Newark, NJ 07102, USA School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455, USA Department of Physics, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand Department of Planetary Sciences, University of Arizona, Tucson, AZ 85721, USA Xiangliang Kong (孔祥良), Fan Guo (郭帆), Chengcai Shen (沈呈彩), Bin Chen (陈彬), Yao Chen (陈耀), Sophie Musset, Lindsay Glesener, Peera Pongkitiwanichakul and Joe Giacalone 2019-12-20 2019-12-20 14:47:10 cgi/release: Article released bin/incoming: New from .zip Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence . Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. yes Nonthermal loop-top sources in solar flares are the most prominent observational signatures that suggest energy release and particle acceleration in the solar corona. Although several scenarios for particle acceleration have been proposed, the origin of the loop-top sources remains unclear. Here we present a model that combines a large-scale magnetohydrodynamic simulation of a two-ribbon flare with a particle acceleration and transport model for investigating electron acceleration by a fast-mode termination shock (TS) at the loop top. Our model provides spatially resolved electron distribution that evolves in response to the dynamic flare geometry. We find a concave-downward magnetic structure located below the flare TS, induced by the fast reconnection downflows. 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