The physics of charged particle acceleration is a key element of theoretical multi-messenger astrophysics. Particles that are accelerated to high energies may indeed escape from the source and thus add up to the cosmic ray spectrum, but they may also interact with ambient fields to produce high-energy neutrinos or photons. In this framework, electromagnetic turbulence plays a central role, because it governs the transport of particles inside the site of acceleration and because it offers itself a promising acceleration process, e.g.through particle-wave interactions.

Since 2013 and the first observation of high-energy astrophysical neutrinos in the IceCube Neutrino Observatory, neutrinos constitute a new messenger to study the extreme Universe, and large neutrino telescopes have been working towards the identification of sources.  While recent multi-messenger observations suggest that blazars may be the first identifiable sources of this observed neutrino flux, other source populations emitting neutrinos remain unidentified.

Le centre de notre galaxie abrite un trou noir super-massif (SMBH) d'environ 4 10⁶ Msol, associé à une source radio compacte appelée Sgr A*. Avec une luminosité bolométrique huit ordres de grandeur en dessous de sa luminosité d'Eddington, son émission actuelle parait très faible. L’émission de Sgr A* présente également des sursauts fréquents (quasi quotidiens) observés du domaine radio aux X-durs. Il apparait maintenant acquis que ces sursauts sont dus à l’accélération rapide d’électrons jusqu’à des énergies dépassant la dizaine de GeV au voisinage du trou noir.

Cosmic rays are relativistic particles that hit continuously the Earth's atmosphere from outer space. Understanding the origin of these cosmic particles, and how they acquire their energy is one of the most important open problems in high energy astrophysics. 

Cosmic rays are high energy particles reaching our planet, whose spectrum  ranges from sub GeV up to 10^10 GeV energies. The bulk of the observed cosmic rays, probably up to PeV energies, is likely of galactic origin and is thought to be accelerated at supernova remnant shocks and to propagate diffusively through the Galaxy. The acceleration mechanism, the escape of accelerated particles from the sources and their subsequent propagation toward us and out of the Galaxy, are all pieces of the same complex puzzle, namely the origin of cosmic rays. A fascinating and yet not understood aspect of