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arXiv · 2211.11054

Solar energetic electron events measured by MESSENGER and Solar Orbiter. Peak intensity and energy spectrum radial dependences: statistical analysis

L. Rodríguez-García·R. Gómez-Herrero·N. Dresing·D. Lario·I. Zouganelis·L. A. Balmaceda·A. Kouloumvakos·A. Fedeli·F. Espinosa Lara·I. Cernuda·G. C. Ho·R. F. Wimmer-Schweingruber·J. Rodríguez-Pacheco
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Abstract

Context/Aims: We present a list of 61 solar energetic electron (SEE) events measured by the MESSENGER mission and the radial dependences of the electron peak intensity and the peak-intensity energy spectrum. The analysis comprises the period from 2010 to 2015, when MESSENGER heliocentric distance varied between 0.31 and 0.47 au. We also show the radial dependencies for a shorter list of 12 SEE events measured in February and March 2022 by spacecraft near 1 au and by Solar Orbiter around its first close perihelion at 0.32 au. Results: Due to the elevated background intensity level of the particle instrument on board MESSENGER, the SEE events measured by this mission are necessarily large and intense; most of them accompanied by a CME-driven shock, being widespread in heliolongitude, and displaying relativistic ($\sim$1 MeV) electron intensity enhancements. The two main conclusions derived from the analysis of the large SEE events measured by MESSENGER, which are generally supported by Solar Orbiter's data results, are: (1) There is a wide variability in the radial dependence of the electron peak intensity between $\sim$0.3 au and $\sim$1 au, but the peak intensities of the energetic electrons decrease with radial distance from the Sun in 27 out of 28 events. On average and within the uncertainties, we find a radial dependence consistent with $R^{-3}$. (2) The electron spectral index found in the energy range around 200 keV ($\delta$200) of the backward-scattered population near 0.3 au measured by MESSENGER is harder in 19 out of 20 (15 out of 18) events by a median factor of $\sim$20% ($\sim$10%) when comparing to the anti-sunward propagating beam (backward-scattered population) near 1 au.

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L. Rodríguez-García, R. Gómez-Herrero, N. Dresing, D. Lario, I. Zouganelis, L. A. Balmaceda, A. Kouloumvakos, A. Fedeli, F. Espinosa Lara, I. Cernuda, G. C. Ho, R. F. Wimmer-Schweingruber, J. Rodríguez-Pacheco. 2022-11-20. Solar energetic electron events measured by MESSENGER and Solar Orbiter. Peak intensity and energy spectrum radial dependences: statistical analysis. https://doi.org/10.1051/0004-6361%2F202244553

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