Fermi-LAT Observation of Quiet Solar Emission

TL;DR

This paper reports Fermi-LAT observations of gamma rays from the quiet Sun, revealing insights into cosmic-ray interactions with solar matter and photons, and analyzing the spectral components during a period of minimal solar modulation.

Contribution

It provides the first detailed spectral analysis of quiet solar gamma-ray emission, distinguishing between disk and inverse Compton components using Fermi data.

Findings

Detection of gamma rays from the quiet Sun due to cosmic-ray interactions

Spectral analysis of disk and inverse Compton components

Correlation with minimal solar modulation period

Abstract

The Large Area Telescope (LAT) on board Fermi has detected high-energy gamma rays from the quiet Sun produced by interactions of cosmic-ray nucleons with the solar surface and cosmic-ray electrons with solar photons in the heliosphere. Such observations provide a probe of the extreme conditions near the solar atmosphere and photosphere and permit the study of the modulation of cosmic rays over the inner heliosphere. For the first year of Fermi observations the solar modulation was at its minimum corresponding to a maximum cosmic-ray flux and, hence, maximum gamma-ray emission from the Sun. We discuss the study of the quiescent solar emission, including spectral analysis of its two components, disk and inverse Compton, using the first-year data of the mission and models using the electron spectrum measured by Fermi.