Electron Energy Spectra and e–e Bremsstrahlung from Anisotropic Electron Distributions in Extreme Solar Flares

• Published in: Geomagnetism and aeronomy Vol. 60; no. 7; pp. 889 - 895
• Main Authors: Oparin, I. D., Charikov, Yu. E., Ovchinnikova, E. P., Shabalin, A. N.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01-12-2020
• Subjects: Earth and Environmental Science; Earth Sciences; Geophysics/Geodesy
• ISSN: 0016-7932; 1555-645X
• DOI: 10.1134/S0016793220070191

We study the electron energy spectra of two powerful solar flares SOL2003-10-28T 1106:16 (
GOES
class X17.2) and SOL2002-07-23T 0018:16 (X4.8) analyzing the HXR and gamma-ray spectra obtained by
RHESSI
. Electron-electron (
e–e
) bremsstrahlung makes a significant contribution to the X-ray flux at energies above 500 keV. In X-ray flux calculations different electron pitch-angle distributions were considered: isotropic, quasi-transverse and quasi-longitudinal. It was shown that breaks in hard X-ray spectra occur on energies ε ≈ 100 keV with photon spectral-index difference Δγ ≥ 1 in the case of quasi-longitudinal anisotropy and hard power-law electron energy spectra. We deduce the parameters of non-thermal electrons energy spectra from
RHESSI
data for the extreme solar flares SOL2003-10-28 and SOL2002-07-23. After including
e–e
bremsstrahlung, the non-thermal electrons energy spectra obtained in the thick-target model can be fitted using power-law with spectral index δ ≈ 5. For the SOL2002-07-23 flare, there is a pronounced asymmetry towards the southern footpoint, starting from energies above 100 keV. The spatial separation of HXR sources at energies above 100 keV may be related to a feature of relativistic electron transport in flaring loops.