Super-massive black holes are known to dwell at the center of galaxies. When accreting matter they are observed from Earth as active galactic nuclei (AGNs). In a minority of AGNs the accretion of matter onto the black-hole is associated with the ejection of a relativistic jet of plasma along the polar axis. 
When the black-hole's jet points right in the direction of the Earth, relativistic effects boost the emission and make these objects among the brightest in the Universe. This peculiar AGNs are called blazars. 

Cette thèse est proposée au sein du groupe d'Astrophysique des Hautes Energies (AHE) du laboratoire APC, qui est cœur du développement de l'astronomie multi-messagers des phénomènes transitoires extrêmes dans l'Univers.