The theoretical activities of the Gamma Ray Astronomy Group are mainly focused on the problem of the origin of Galactic cosmic rays.
Cosmic rays are energetic charged particles (mainly protons) that fill the whole Galaxy. We observe them at the Earth as an isotropic diffuse flux of particles. The isotropy is due to the fact that the turbulent interstellar magnetic field deflects particles, and prevents us to identify the sources of cosmic rays by looking at the particles' arrival direction.
Diffusive shock acceleration operating at expanding supernova remnant shells is by far the most popular model for the origin of galactic cosmic rays. Despite the general consensus received by the model, an unambiguous and conclusive proof of the supernova remnant hypothesis is still missing. In this context, the recent developments in gamma ray astronomy provide us with precious insights into the problem of the origin of galactic cosmic rays, since production of gamma rays is expected both during the acceleration of cosmic rays at supernova remnant shocks and during their subsequent propagation in the interstellar medium. In particular, the recent detection of a number of supernova remnants at TeV energies nicely fits with the model, but it still does not constitute a conclusive proof of it, mainly due to the difficulty of disentangling the hadronic and leptonic contributions to the observed gamma ray emission.
Within this framework, the study of the gamma-ray radiation produced by cosmic rays that escape supernova remnants is of paramount importance for (at least) two reasons: first, the detection of those gamma-ray photons can serve to identify the sources of cosmic rays and, second, the characteristics of that radiation give us constraints on the way in which cosmic rays propagate in the interstellar medium.
Besides that, the group is also active in the theoretical study of extragalactic objects such as active galactic nuclei and clusters of galaxies, and also in the quest for the sources of the ultra high energy cosmic rays that cannot be confined within the Galaxy and are most likely of extra-galactic origin.
You would like to know more? Please contact Stefano Gabici