FLUKA simulations of pion decay gamma-radiation from energetic flare ions

MacKinnon, A. , Szpigel, S., Gimenez de Castro, G. and Tuneu, J. (2020) FLUKA simulations of pion decay gamma-radiation from energetic flare ions. Solar Physics, 295, 174. (doi: 10.1007/s11207-020-01699-9)

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Gamma-ray continuum at >10 MeV photon energy yields information on ≳0.2 – 0.3 GeV/nucleon ions at the Sun. We use the general-purpose Monte Carlo code FLUktuierenden KAskade (FLUKA) to model the transport of ions injected into thick and thin target sources, the nuclear processes that give rise to pions and other secondaries and the escape of the resulting photons from the atmosphere. We give examples of photon spectra calculated with a range of different assumptions about the primary ion velocity distribution and the source region. We show that FLUKA gives results for pion decay photon emissivity in agreement with previous treatments. Through the directionality of secondary products, as well as Compton scattering and pair production of photons prior to escaping the Sun, the predicted spectrum depends significantly on the viewing angle. Details of the photon spectrum in the ≈100 MeV range may constrain the angular distribution of primary ions and the depths at which they interact. We display a set of thick-target spectra produced making various assumptions about the incident ion energy and angular distribution and the viewing angle. If ions are very strongly beamed downward, or ion energies do not extend much above 1 GeV/nucleon, the photon spectrum is highly insensitive to details of the ion distribution. Under the simplest assumptions, flares observed near disc centre should not display significant radiation above 1 GeV photon energy. We give an example application to Fermi Large Area Telescope data from the flare of 12 June 2010.

Item Type:Articles
Glasgow Author(s) Enlighten ID:MacKinnon, Dr Alexander and Tuneu, Mr Jordi
Authors: MacKinnon, A., Szpigel, S., Gimenez de Castro, G., and Tuneu, J.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Solar Physics
ISSN (Online):1573-093X
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Solar Physics 295: 174
Publisher Policy:Reproduced under a Creative Commons License

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