International School of Cosmic Ray Astrophysics <<Maurice M. Shapiro>>

21^st Course: Astroparticle Physics: Yesterday, Today, and Tomorrow
1-7 August, 2018

Gamma-ray astronomy explores the most powerful phenomena in the Universe, addressing fundamental questions in particle astrophysics ranging from powerful astrophysical jets and extreme physics of compact objects to the nature of dark matter and origin of gamma-ray bursts. The Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Observatory, launched in 2008, has collected more than a billion photons in the energy range from 100 MeV to 1 TeV and provided transformational observations of the high-energy gamma-ray sky. Observations by Fermi have increased the number of known high-energy gamma-ray sources to more than 3000 and revealed diffuse gamma-ray emission with unprecedented detail. In my lecture I will review some of the new results, focusing on the search for dark matter, GeV gammarays from the Galactic Center region and observations of cosmic-ray electrons. I will also discuss the importance and perspectives in the search for electromagnetic counterparts to gravitational wave detection of binary mergers that include at least one neutron star. I will also discuss new horizons in this field. In the energy range above 100 MeV, Fermi LAT continues to be the premier multi-purpose observatory. However, the lower energy range, from a few hundred keV to ~100 MeV, remains largely unexplored since the pioneering but limited observations by COMPTEL onboard CGRO (1991-2000). I will discuss the science objectives and potential future missions in this energy range which is full of potential discoveries.