Two Phases of Solar Flares and a Stochastic Mechanism for Acceleration of Electrons and Protons
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TWO PHASES OF SOLAR FLARES AND A STOCHASTIC MECHANISM FOR ACCELERATION OF ELECTRONS AND PROTONS
A. B. Struminsky,1 I. Yu. Grigorieva,2 Yu. I. Logachev,3 and A. M. Sadovski1
The hypothesis of two phases of charged particle acceleration in solar flares is well known, with subrelativistic electrons accelerated in the first phase and relativistic electrons and protons in the second. Both phases are distinguished in the solar proton events and their parent flares of December 26, 2001 (M7.1), November 2, 2003 (X8.3), and August 9, 2011 (X6.9), while in the interplanetary space only electrons were observed from the first phase and electrons and protons from the second. The temporal profiles of the electrons and protons from the second phase are similar; hence, it is concluded that the relativistic electrons and protons observed in the interplanetary space are predominantly accelerated in flares, rather than in the shock front of a coronal mass ejection. Most likely a stochastic acceleration mechanism is realized in flares where protons and electrons gain energy in many elementary events over the entire duration of the flare which lasts much longer than an elementary event. To ensure consistency of a stochastic acceleration process with the existence of two phases in solar flares it is necessary to consider gyrosynchronous radiative electron losses in the second phase which can be neglected in the first phase. The energy of the accelerated protons in the first phase is small for their detection in processes taking place on the sun, but in the second phase it may be sufficient to produce gamma lines, both nuclear and from pion decay. Keywords: solar flares: X-ray and radio emission: coronal mass ejection: acceleration of solar protons and electrons: solar electron and proton events
(1) Space Research Institute, Russian Academy of Sciences, Moscow; e-mail: [email protected] (2) Main (Pulkovo) Astronomical Observatory, Russian Academy of Sciences, St. Petersburg (3) M. V. Lomonosov Moscow State University, D. V. Skobel’tsyn Scientific Research Institute of Nuclear Physics, Moscow, Russia
Original article submitted September 6, 2019; accepted for publication June 24, 2020. Astrofizika, Vol. 63, No. 3, pp. 437-449 (August 2020) 388
0571-7256/19/6303-0388 ©2020 Springer Science+Business Media, LLC
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1. Introduction
The solar proton events of September 4, 6, and 10, 2017 stirred us to turn again to the hypothesis of two phases of charged particle acceleration in flares [1-3] where electrons with energies 100 keV and protons, in the second. In these events, data from the SOHO/EPHIN detector (relativistic electrons) and the Anti-coincidence shield of the spectrometer on the INTEGRAL spacecraft (ACS SPI, >100 MeV protons were used to distinguish electrons and protons near the earth accelerated in the first and second phases of the flares [4-6]. It turned out that after the flares X9.3 of September 6 and X8.2 of September 10, 2017, both electrons accelerated in the first phase and electrons and protons from th
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