Solar Electrons and Protons in the Events of September 4-10, 2017 and Related Phenomena

摘要

The solar proton events on September 4-10, 2017 motivated us to reconsider the hypothesis of the presence of two phases of acceleration of charged particles in solar flares in which nonrelativistic electrons are accelerated in the first phase, while relativistic electrons and protons are accelerated during the second phase. According to the data of SOHO/EPHIN (relativistic electrons) and ACS SPI (hard X-rays and protons with energy of >100 MeV), the populations of electrons and protons accelerated at the first and second phases of a flare could be separated in these events near the Earth. The data of observations are indicative of the realization of a stochastic mechanism of acceleration in flares according to which protons and electrons gain energy in many elementary acts, whose duration is much shorter than that of the flare itself. To reconcile the stochastic acceleration process with the existence of two phases in solar flares, it is necessary taking into account the gyrosynchrotron radiation losses of electrons that can be neglected at the first phase. The energy of accelerated protons at the first phase is too low for their detection in the Sun. However, in the second phase, it can reach levels sufficient for detection of nuclear and pion decay gamma lines. In this case, the role of coronal mass ejection consists in (1) involvement of an increasingly larger number of loops in the flare process at altitudes ranging from the chromosphere to the corona; (2) return of the accelerated particles into the flare region; (3) additional acceleration of particles at the shock front; (4) creation of conditions for escaping of particles into the interplanetary space in a wide spatial angle.