Astrophysique à Haute Energie

First Real-time Multi-Energy Neutrino follow up

The Astroparticle physics groups hosted at the Centre for Cosmology, Particle Physics and Phenomenology (CP3) at UCLouvain (Belgium) and at the Laboratoire Astroparticule et Cosmologie (APC) at Université Paris Cité (UPCité) are welcoming applications for a joint PhD student position in multi-messenger astronomy, to work on the joint detection of neutrinos and gravitational waves.

The nature of extreme particle accelerators in the Galaxy

Tremendous advances in our knowledge of the origin of Galactic cosmic-rays (CR) have been made during the last decades. In particular, shock acceleration theory and observations with X-ray and gamma-ray have confirmed that the remnants of supernova explosions do accelerate particles. But so far, no evidence supports their ability to produce particles up to the knee energy of CRs around the PeV range. Gamma-rays in the very high energy (VHE, around the TeV) and ultra-high energy (UHE, beyond 100 TeV) domains are the key observables to search for extreme Galactic accelerators. 

Photon and neutrino multi-messenger emission from active galactic nuclei

There is a general consensus that every galaxy harbors a supermassive black hole (SMBH) at its nucleus. While we cannot easily study these exotic objects directly, we can investigate how they interact with their surroundings. When an SMBH accretes matter, it becomes active and starts radiating, primarily emitting thermal photons from the accretion disk that feeds it. These accreting SMBHs, known as Active Galactic Nuclei (AGNs), are among the brightest sources of photons in the Universe.

Study of accretion-ejection processes in the vicinity of black holes with SVOM and Einstein Probe

Supermassive black holes (SMBHs) located at the center of galaxies, particularly those powering luminous Active Galactic Nuclei (AGNs), and stellar-mass black holes in X-ray bright binary systems (XRBs), exhibit highly variable and often transient X-ray and gamma-ray emissions. Additionally, Tidal Disruption Events (TDEs) —which occur when a star approaches a massive black hole and is tidally disrupted— produce electromagnetic ares peaking in the UV and soft X-rays. 

Constraining Cosmic-Ray Acceleration through Multi-Messenger Model Fitting and Early CTAO Science

The origin of cosmic rays represents a major missing block in our understanding of the Universe. The main challenge we face is that, being charged, they are deviated in their journey from their natural accelerator to the Earth. There is however an indirect way to study their acceleration sites: wherever a cosmic ray is accelerated to high energies, it unavoidably interacts with its environment, leading to the production of photons and neutrinos. These by-products can travel along geodesics and can thus directly point to the loci of particle acceleration in the Universe.

Testing the energy dependence of the Cosmic-Ray gradient in the Galactic Centre

The Galactic Centre (GC) is a unique astrophysical environment dominated by extreme objects such as the supermassive black hole (SMBH) Sgr A* and three of the most massive  young star clusters in the Galaxy. Gamma-ray observations of interstellar gamma-ray emission using the High Energy Stereoscopic System (HESS) have revealed that a quasi-steady source near the GC injects energetic cosmic rays (CRs) into the surrounding region. These CRs propagate through the inner 200 parsecs (pc) of the Galaxy, creating a gradient in cosmic ray density. 

Seyfert galaxies as gamma-ray and neutrino sources

The origin of cosmic-rays remains one of the most important open questions in astrophysics. A powerful tool to study their acceleration sites are multi-messenger (photons and neutrinos) observations: wherever a cosmic-ray (a proton or an atomic nucleus) is accelerated, it interacts with its environment producing pions that then decay into photons, neutrinos and electrons.  γ and ν can escape the region and travel on geodesics to Earth, pinpointing their source in the Universe. 

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