Double-power-law Feature of Energetic Particles Accelerated at Coronal Shocks

Journal Article · 30 January 2022 · The Astrophysical Journal. Letters

DOI: https://doi.org/10.3847/2041-8213/ac4cb3 · OSTI ID:2005824

Yu, Feiyu  ^[1]; Kong, Xiangliang  ^[1]; Guo, Fan  ^[2]; Liu, Wenlong ^[1]; Jiang, Zelong ^[1]; Chen, Yao  ^[1]; Giacalone, Joe  ^[3]

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1. Shandong Univ. (China)
2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States)
3. Univ. of Arizona, Tucson, AZ (United States)

Recent observations have shown that in many large solar energetic particle (SEP) events the event-integrated differential spectra resemble double power laws. We perform numerical modeling of particle acceleration at coronal shocks propagating through a streamer-like magnetic field by solving the Parker transport equation, including protons and heavier ions. We find that for all ion species the energy spectra integrated over the simulation domain can be described by a double power law, and the break energy depends on the ion charge-to-mass ratio as E_B ~ (Q/A)^α, with α varying from 0.16 to 1.2 by considering different turbulence spectral indices. We suggest that the double-power-law distribution may emerge as a result of the superposition of energetic particles from different source regions where the acceleration rates differ significantly due to particle diffusion. The diffusion and mixing of energetic particles could also provide an explanation for the increase of Fe/O at high energies as observed in some SEP events. Although further mixing processes may occur, our simulations indicate that either a power-law break or rollover can occur near the Sun and predict that the spectral forms vary significantly along the shock front, which may be examined by upcoming near-Sun SEP measurements from the Parker Solar Probe and Solar Orbiter.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Laboratory Directed Research and Development (LDRD) Program
• Grant/Contract Number: 89233218CNA000001; SC0020219
• OSTI ID: 2005824
• Report Number(s): LA-UR--21-27255
• Journal Information: The Astrophysical Journal. Letters, Journal Name: The Astrophysical Journal. Letters Journal Issue: 2 Vol. 925; ISSN 2041-8205
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English