ETD

• astrophysical jets
• gamma-ray emission
• micro-quasars
• particle acceleration
• shock acceleration

This thesis investigates particle acceleration mechanisms that may occurs in the jets of microquasars aiming at estimate the very high energy emission in gamma-rays produced by hadronic interaction between accelerated particles and the gas located around the sources. Microquasars are Galactic sources consisting of a star and a compact object that accretes matter through an accretion disk. The recent detection of photons with energies exceeding 100 TeV from some of these sources has brought them back to the forefront of high-energy astrophysics. The present work focuses on the source SS433.
The analysis begins with a geometrical description of the jet-cocoon system and its temporal evolution. The system is divided into three distinct regions: the jet base, the jet head and the cocoon.
Within this framework, a model is developed to describe particle acceleration at different shocks present in the system, namely the recollimation shock at the jet base and the reverse and forward shocks at the jet head.
By solving the space-dependent transport equation, the particle distributions in the different region is obtained , as well as robust predictions for the maximum energies achievable as a function of the intrinsic properties of the system. In particular solving the transport equation inside the cocoon, it is possible to estimate the number of particles that escape the system. These escaping particles interact with the gas cloud surrounding the source through proton-proton (pp) interactions, which produce pions whose decay gives rise to gamma-ray photons. Finally, the model is applied to a few microquasars that have been recently detected in gamma-rays by the LHAASO observatory, and the conditions under which the model can account for the detected emission are discussed.