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

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Abstract

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.

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Authors and Affiliations

  1. Ioffe Institute, St. Petersburg, Russia

    I. D. Oparin, Yu. E. Charikov, E. P. Ovchinnikova & A. N. Shabalin

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  1. I. D. Oparin
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  2. Yu. E. Charikov
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  3. E. P. Ovchinnikova
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  4. A. N. Shabalin
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Correspondence to I. D. Oparin.

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Oparin, I.D., Charikov, Y.E., Ovchinnikova, E.P. et al. Electron Energy Spectra and e–e Bremsstrahlung from Anisotropic Electron Distributions in Extreme Solar Flares. Geomagn. Aeron. 60, 889–895 (2020). https://doi.org/10.1134/S0016793220070191

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  • DOI: https://doi.org/10.1134/S0016793220070191

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