Fermi Gamma-ray Space Telescope

Fermi LAT observations of the lunar gamma-ray emission

F. Loparco
M. N. Mazziotta, on behalf of the Fermi LAT Collaboration

Abstract:

We have measured the gamma-ray emission spectrum of the Moon using the data collected by the Large Area Telescope onboard the Fermi satellite during its first 7 years of operation in an energy range from 30 MeV up to a few GeV. Gamma rays emitted from the Moon originate in the hadronic interactions of cosmic-ray nuclei with the lunar surface. To explain our results, we have developed a full Monte Carlo simulation, based on the FLUKA code, describing the interactions of different species of cosmic-ray nuclei with the lunar surface and the subsequent production of gamma rays. From our simulation we evaluated the lunar gamma-ray spectrum in the epoch when direct measurements of the cosmic-ray proton and helium spectra performed by AMS-02 were available. The predictions from the simulation are in good agreement with our observations, thus confirming the reliability of our model. Finally, starting from a model for the local interstellar spectra of cosmic rays, we have used our simulation to study the solar modulation from the lunar gamma-ray data.