Radiative Acceleration and Emission from Relativistic Outflows

June 2018Outflowing streams of matter or jets are a common phenomenon in the observed\ud universe. The most extreme and powerful jets are relativistic, i.e., they travel at speeds\ud comparable to the of speed light. Gamma Ray-Bursts (GRBs) and Active Galactic Nuclei\ud (AGNs) are two sources of these relativistic jets. In this work I will explore the role played\ud by advected radiation the radiation internal to the jet itself in modifying the jet\ud dynamics and creating the observed radiation spectrum. First, I present a Monte Carlo\ud code designed to simulate the spectrum formed in a scattering dominated photon-lepton\ud plasma. I demonstrate that non-thermal features in the emitted spectrum can arise\ud from the interaction of thermal populations of photons and leptons, initially at different\ud temperatures. I find the existence of a correlation between the spectral parameters\ud that suggests the presence of this mechanism in cosmic sources, for example, in prompt\ud spectra of GRBs. These simulations, however, do not account for the dynamical coupling\ud between the radiation and matter within the jet, which is expected for outflows from both\ud GRBs and AGNs. In the second part of this dissertation, I show how radiation regulates\ud the dynamical properties (such as structure, acceleration) of jets. I use a custom-made\ud dynamic Monte Carlo code to study radiation (Compton scattering) driven expansion\ud and acceleration in unexplored evolutionary stages of GRB jets. My results uncover new\ud regimes of jet evolution and allow me to obtain analytical estimates to better parameterize\ud the jet dynamics in analytical and semi-analytical studies. In addition, I explore radiative\ud acceleration and deceleration as mechanisms to produce two-component structured AGN\ud jets. I find that this radiation-driven regulatory mechanism plays a crucial role in\ud explaining the puzzling observation of high-energy emission from misaligned AGN jets