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On some features of the solar proton event on 2021 October 28 (GLE73)
In addition to several recent articles devoted to the rare event of
ground-level enhancement of the solar relativistic proton flux observed on 2021
October 28 (GLE73), we study the 10-100 MeV solar energetic particle (SEP)
component of this event. Based on the GOES satellite data for 26 GLEs recorded
since 1986, we have formed a scatter plot displaying the ratio of the peak
fluxes of the >10 MeV (J10) and >100 MeV (J100) protons and their energy
spectra. Two extreme characteristics of the prompt component of the SEP-GLE73
event were revealed: (1) very small J10 and J100 proton fluxes and (2) a very
hard energetic spectrum in the 10-100 MeV range. There are only two events with
these characteristics similar to SEP-GLE73 namely, GLE40 (1989 July 25) and
GLE46 (1989 November 15). A correspondence was demonstrated between the hard
frequency spectrum of microwave radio bursts of initiating flares and the hard
SEP energy spectrum of these two and other GLEs. These results suggest that the
flare magnetic reconnection both in the impulsive and post-eruption phases
plays an important role in the acceleration of the SEP-GLE protons.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in MNRA
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