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Positron Processes in the Sun

Solar Physics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Atoms 2020, 8(2), 14;
Received: 19 March 2020 / Revised: 8 April 2020 / Accepted: 16 April 2020 / Published: 22 April 2020
(This article belongs to the Special Issue Interactions of Positrons with Matter and Radiation)
Positrons play a major role in the emission of solar gamma-rays at energies from a few hundred keV to >1 GeV. Although the processes leading to positron production in the solar atmosphere are well known, the origin of the underlying energetic particles that interact with the ambient particles is poorly understood. With the aim of understanding the full gamma-ray spectrum of the Sun, I review the key emission mechanisms that contribute to the observed gamma-ray spectrum, focusing on the ones involving positrons. In particular, I review the processes involved in the 0.511 MeV positron annihilation line and the positronium continuum emissions at low energies, and the pion continuum emission at high energies in solar eruptions. It is thought that particles accelerated at the flare reconnection and at the shock driven by coronal mass ejections are responsible for the observed gamma-ray features. Based on some recent developments I suggest that energetic particles from both mechanisms may contribute to the observed gamma-ray spectrum in the impulsive phase, while the shock mechanism is responsible for the extended phase. View Full-Text
Keywords: solar flares; coronal mass ejections; shocks; positrons; positronium; positron annihilation; pion decay solar flares; coronal mass ejections; shocks; positrons; positronium; positron annihilation; pion decay
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Gopalswamy, N. Positron Processes in the Sun. Atoms 2020, 8, 14.

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