Solar Gamma-Ray Flares and Activity Complexes
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r Gamma-Ray Flares and Activity Complexes V. M. Tomozova, S. A. Yazeva, b, *, and E. S. Isaevaa, b a Institute
of Solar–Terrestrial Physics, Siberian Branch, Russian Academy of Sciences, Irkutsk, Russia b Irkutsk State University, Irkutsk, Russia *e-mail: [email protected] Received January 13, 2020; revised April 21, 2020; accepted April 30, 2020
Abstract—Strong flare events with an extended phase of gamma ray emission from the catalog by Share et al. have been analyzed in order to explain the characteristics of the impulsive and extended phases of such flares and reveal their connection with activity complexes and coronal holes. It is shown that 74% of such events are closely related to activity complexes. It has been qualitatively demonstrated that the particle acceleration processes during the flare development are associated with the changes in the magnetic topology of the flare region and the evolution of the coronal mass ejection. The possible relation of coronal holes to activity complexes and the role of “exchange” reconnection in these processes are discussed. DOI: 10.1134/S1063772920090073
INTRODUCTION Gamma radiation of solar origin was first detected during strong solar flares on August 4 and 7, 1972 by the American space observatory OSO-7 [1]. Currently, continuous extra-atmospheric monitoring of solar gamma radiation is performed. It appears that gamma radiation sources are observed rather rarely, on the order of tens of events per cycle, i.e., they are manifested in a rather small number of solar flares [2]. The origination of gamma-ray sources in solar flares is traditionally associated with nuclear interactions that occur in the solar atmosphere under certain conditions. According to results [3], when flare-accelerated protons and other ions with energies above 300 MeV interact with the solar atmosphere’s plasma, this can lead to the occurrence of neutral and charged pions. The decay of neutral pions results in the generation of high-energy gamma rays (>70 MeV), which form a wide spectrum of emission with a maximum around 70 MeV that is sometimes detected by spacecraft instruments. Thus, the occurrence of gamma radiation requires fluxes of high-energy protons under certain quite specific conditions, which are realized during some flares. In recent years, much attention has been paid to the study of flares with an extended phase of gamma emission, which are relatively strong and geoeffective events. They are almost always accompanied by fast halo-type coronal mass ejections (CMEs). A number of previous papers [4–6] was dedicated to the study of solar activity complexes (ACs) and their geoeffective manifestations. ACs are long-lived (from 3 to 17 solar rotations) magnetic field systems. They appear as regions of continuous sunspot formation in the zones
with the same heliographic coordinates. At the maximum of their development, ACs can be complex magnetic configurations of interacting active regions (ARs). In the ACs, the most powerful flares are generated, as well as high-speed CMEs, which can eff
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