Self-consistent Modeling of Gamma-ray Spectra from Solar Flares with the Monte Carlo Simulation Package FLUKA

Abstract

We use the Monte Carlo particle physics code FLUKA (Fluktuierende Kaskade) to calculate γ-ray spectra expected from solar flare energetic ion distributions. The FLUKA code includes robust physics-based models for electromagnetic, hadronic and nuclear interactions, sufficiently detailed for it to be a useful tool for calculating nuclear de-excitation, positron annihilation and neutron capture line fluxes and shapes, as well as ≈ GeV continuum radiation from pion decay products. We show nuclear de-excitation γ-ray line model spectra from a range of assumed primary accelerated ion distributions and find them to be in good agreement with those found using the code of Murphy et al. (2009). We also show full γ-ray model spectra which exhibit all the typical structures of γ-ray spectra S.

FLUKA Simulations of Pion Decay Gamma-Radiation from Energetic Flare Ions

“…In z > 0 there is a uniform density "atmosphere" of solar (Asplund et al, 2009) composition. While a stratified density structure was implemented in Tusnski et al (2019), total thick target yields are insensitive to the detailed density structure so this simple model is adequate for our purposes here. The total depth of the atmosphere in z and its lateral extent in x and y were made big enough to ensure all particles stop and produce their thick target yields within it.…”

“…As described in Tusnski et al (2019) we wrote a custom subroutine to simulate particles coming from a power-law energy distribution between two fixed energies E min and E max :…”

“…Here we show a set of simulated backward hemisphere gamma-ray spectra from primary protons injected with power-law energy distributions and the angular distributions specified in Equations 3 above. We concentrate on the continuum spectrum, above 10 MeV; line features at lower energies were discussed by Tusnski et al (2019). For now spectra are averaged over the viewing angle but we discuss directionality in the next section.…”

“…determine the energy deposited in a particular volume, or the flux of particles of a particular type crossing the boundary between two regions. It was introduced as a tool for modelling solar flare gammaradiation by Tusnski et al (2019). Here we will use FLUKA to predict the gamma-ray continuum radiation 10 MeV resulting from hypothesised energetic ion distributions interacting with the solar atmosphere and illustrate how these simulated spectra may be used to interpret observed gamma-ray spectra.…”

“…Its authors aim in the first instance to provide treatments of all the processes taking place, to the same degree of precision, rather than to offer the user a set of disconnected modules each providing its own treatment of a particular physical process. As a consequence it can be used to simulate a single, self-consistent gamma-ray spectrum extending from the positron annihilation line at 0.511 MeV through the nuclear deexcitation line component at ≈ 1 -7 MeV, to the pion decay continuum in the GeV energy range (Tusnski et al, 2019). Nonetheless mechanisms are provided to, e.g., suppress some of the full set of processes taking place, even if this is strictly unphysical, and these prove very useful in developing physical understanding.…”