The first self-consistent simulations of electron acceleration during magnetic reconnection in a macroscale system are presented. Consistent with solar flare observations, the spectra of energetic electrons take the form of power laws that extend more than two decades in energy. The drive mechanism for these nonthermal electrons is Fermi reflection in growing and merging magnetic flux ropes. A strong guide field suppresses the production of nonthermal electrons by weakening the Fermi drive mechanism. For a weak guide field the total energy content of nonthermal electrons dominates that of the hot thermal electrons even though their number density remains small. Our results are benchmarked with the hard x-ray, radio, and extreme ultraviolet observations of the X8.2-class solar flare on September 10, 2017.
Bibliographical noteFunding Information:
The collaboration leading to these results was facilitated by the NASA Drive Science Center on Solar Flare Energy Release (SolFER), Grant No. 80NSSC20K0627. We would like to thank Dr. W. Daughton and participants in the NASA Drive Center SolFER for invaluable discussions that contributed to this work. This work has been supported by NSF Grants No. PHY1805829 and No. PHY1500460 and the FIELDS team of the Parker Solar Probe (NASA Contract No. NNN06AA01C) and the FINESST Grant No. 80NSSC19K1435. Fan Guo acknowledges support in part from NASA Grant No. 80NSSC20K1318 and Astrophysics Theory Program, and DOE support through the LDRD program at LANL. Joel Dahlin was supported by an appointment to the NASA Postdoctoral Program at the NASA Goddard Space Flight Center, administered by Universities Space Research Association under contract with NASA. The simulations were carried out at the National Energy Research Scientific Computing Center (NERSC). The data used to perform the analysis and construct the figures for this Letter are preserved at the NERSC High Performance Storage System and are available upon request. E. K. acknowledges financial support from the STFC Consolidated Grant No. ST/T000422/1. M. S. acknowledges support in part from NASA Grant No. 80NSSC20K1277.
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