In the solar corona charged particles can be accelerated during major events of magnetic restructuring, i.e. flares and coronal mass ejections. On occasion protons are observed to attain energies well above 1 GeV. These particles can be probed through their radiative signatures, while particles escaping from the corona can be probed by space-borne or ground-based detectors. A number of acceleration scenarios have been devised related to magnetic reconnection in complex magnetic fields and to shock waves driven by ejected large-scale magnetic structures. In this talk I will attempt to give an overview on the scenarios and to show how observations of energetic electrons at hard X-ray and radio wavelengths, and in situ measurements of energetic particles near the Earth constrain them. A simple acceleration scenario will be illustrated for numerous rather short solar events, while the most energetic events require a more complex and time-extended process that many believe to be related to shock acceleration. I will especially discuss the most energetic particle signatures from the Sun, through a comparison of gamma-ray observations by Fermi/LAT and in situ measurements on the Earth by neutron monitors of relativistic protons, and try to identify observational signatures pointing to the region and the process of acceleration. New possibilities of investigation come especially from space missions that approach the Sun, Parker Solar Probe (NASA) and Solar Orbiter (ESA/NASA).
Karl-Ludwig Klein
Observatoire de Paris, LESIA
