The 2009 Fermi Symposium

Fermi-LAT Observation of the Gamma-ray Emission from the Sun

Elena Orlando

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 surface 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 the maximum cosmic-ray flux and, hence, 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. Results are compared with theoretical models of solar modulation and previous observations with the EGRET instrument.