Solar gamma rays and modulation of cosmic rays in the inner heliosphere

TL;DR

This paper reviews gamma-ray emissions from the Sun caused by cosmic rays, discusses updated models of inverse Compton emission based on solar activity, and predicts detection prospects for upcoming gamma-ray missions.

Contribution

It provides new models of solar inverse Compton gamma-ray emission incorporating recent cosmic ray measurements and forecasts detection capabilities of future gamma-ray observatories.

Findings

Inverse Compton emission varies with solar activity levels.

Models align with cosmic ray data across different solar conditions.

Predictions suggest detectability by future gamma-ray missions.

Abstract

The first evidence of the gamma-ray emission from the quiescent Sun was found in the archival EGRET data that was later confirmed by Fermi-LAT observations with high significance. This emission is produced by Galactic cosmic rays (CRs) penetrating the inner heliosphere and inter- acting with the solar atmosphere and optical photons. The solar emission is characterized by two spatially and spectrally distinct components: (i) disk emission due to the CR cascades in the solar atmosphere, and (ii) spatially extended inverse Compton (IC) emission due to the CR electrons scattering off of solar photons. The intensity of both components associated with Galactic CRs anti-correlate with the level of the solar activity being the brightest during solar minimum. In this paper we discuss updates of the models of the IC component of the emission based on CR measurements made at different levels of solar activity, and we make predictions for e- ASTROGAM and AMEGO, proposed low-energy gamma-ray missions.