Energetic gamma-ray emission from solar flares

TL;DR

This paper updates gamma-ray flux models for solar flares using new pion production cross sections, revealing different spectral parameters and emphasizing the importance of nuclei and low-energy data in understanding flare emissions.

Contribution

It introduces revised interaction models for gamma-ray flux computation, incorporating nuclei and low-energy data, leading to more accurate spectral parameter inference.

Findings

Spectral parameters differ significantly with new cross sections.

Including nuclei results in a harder primary spectrum.

Low-energy flare data enhances spectral understanding.

Abstract

Recent advances in the $\gamma$-ray observations of solar flares by the \textit{Fermi} satellite, demand revisions in the hadronic $\gamma$-ray flux computation below 1 GeV. In this work we utilize recently updated pion production cross sections, along with an accurate description of low energy nuclear interactions. Applying these new interaction descriptions to model the \textit{Fermi} Large Area Telescope (LAT) solar flare data, we infer the primary particle spectral parameters. Application of this new cross section description leads to significantly different spectral parameters compared to those obtained previously. Furthermore, the inclusion of nuclei in these calculations leads to a primary spectrum that is generally harder than that required from proton only considerations. Lastly, the flare data at lower MeV energies, detected by the \textit{Fermi} Gamma-ray Burst Monitor (GBM), is demonstrated to provide additional low-energy spectral information.