Astrophysique à Haute Energie

Resumé

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. Among promising candidates are short gamma-ray bursts (SGRBs) resulting from the merger of two neutron stars.

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.

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.

Stars form due to the gravitational collapse of dense molecular clouds. The process of star formation is still not completely understood, but it is believed that a crucial parameter that regulates star formation is the ionization level in the dense cores of molecular clouds. This is because the ionization level is determining the coupling between the gas and the magneticl field, which is in turn affecting the dynamics of the collapse through magnetic pressure support.

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. 

The origin of PeV cosmic rays is a crucial issue in cosmic ray physics. The chemical composition of cosmic rays is dominated by protons below a particle energy of ~1 PeV, while heavier nuclei become important above it. This, together with the evidence that the transition between galactic and extragalactic cosmic rays takes place at particle energies largely exceeding the PeV, implies that the sources of galactic cosmic rays must be proton PeVatrons