Charge-to-mass dependence of heavy ion spectral breaks in large gradual solar energetic particle events

15th Annual International Astrophysics Conference: "The Science of Ed Stone: Celebrating his 80th Birthday"

物理学;天文学

Desai, M.I.^1,2 ; Mason, G.M.^3 ; Dayeh, M.A.^1 ; Ebert, R.W.^1 ; McComas, D.J.^4 ; Li, G.^5 ; Cohen, C.M.S.^6 ; Mewaldt, R.A.^6 ; Schwadron, N.A.^7 ; Smith, C.W.^7

Southwest Research Institute, 6220 Culebra Road, San Antonio

TX

78023, United States^1

University of Texas at San Antonio, One UTSA Circle, San Antonio

TX

78249, United States^2

Johns Hopkins University, Applied Physics Laboratory, Laurel

MD

20723, United States^3

Department of Astrophysical Sciences, Princeton University, NJ

08544, United States^4

CSPAR, University of Alabama in Huntsville, Huntsville

AL

35756, United States^5

California Institute of Technology, Pasadena

CA

91125, United States^6

University of New Hampshire, 8 College Road, Durham

NH

03824, United States^7

关键词: Energy parameters;    Extreme events;    Interplanetary turbulence;    Kolmogorov turbulence;    Normalization constants;    Solar energetic particle events;    Spectral slopes;    Wave intensities;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/767/1/012004/pdf
DOI  :  10.1088/1742-6596/767/1/012004

学科分类：天文学(综合)

来源: IOP

【 摘 要 】

We fit the ∼0.1-500 MeV/nucleon H-Fe spectra in 46 large SEP events surveyed by [1] with the double power-law Band function to obtain a normalization constant, low- and high-energy parameters γaand γb; and break energy EB. We also calculate the low-energy power-law spectral slope γ1. We find that: 1) γa, γ1, and γbare species-independent within a given SEP event, and the spectra steepen with increasing energy; 2) EB's are well ordered by Q/M ratio, and decrease systematically with decreasing Q/M, scaling as (Q/M)αwith α varying between ∼0.2-3; 3) α is well correlated with Fe/O at ∼0.16-0.23 MeV/nucleon and CME speed; 4) In most events: α b-γa>3; and 5) Seven out of nine extreme SEP events (associated with faster CMEs and GLEs) are Fe-rich and have α >1.4 with flat spectra at low and high energies yielding γb-γaa, γ1, and γband the systematic Q/M dependence of EBwithin an event, as well as the range of values for α suggest that the formation of double power-laws in SEP events occurs primarily due to diffusive acceleration at near-Sun CME shocks and not due to scattering in the interplanetary turbulence. In most events, the Q/M-dependence of EBis consistent with the equal diffusion coefficient condition while the event-to-event variations in a are probably driven by differences in the near-shock wave intensity spectra, which are flatter than the Kolmogorov turbulence spectrum but still weaker compared to that inferred for the extreme events. The weaker turbulence allows SEPs to escape more easily, resulting in weaker Q/M-dependence of EB, (lower a values) and spectral steepening at higher energies. In extreme events, the flatter spectra at high- and low-energy and stronger Q/M-dependence of EB(larger α values) occur due to enhanced wave power, which also enables the faster CME shocks to accelerate flare suprathermals more efficiently than ambient coronal ions.