Short and Long GRBs with Simultaneous Thermal and Non-Thermal Emission Signatures: Laboratories for Studying the Dynamics of Relativistic Jets.

In the vast majority of Gamma-Ray Bursts (GRBs), it is difficult to unambiguously identify the emission processes powering their prompt emission; this is a strong limitation to the interpretation of the physics of the phenomenon. However, some short and long GRBs display clear signatures of simultaneous thermal and non-thermal emissions. These GRBs are ideal laboratories for disentangling the emission components, studying their spectral shapes, and extracting physical quantities characterizing their relativistic jets. In this presentation, I will focus on a sample of short and long GRBs observed with the Gamma-ray Burst Monitor on-board the Fermi Gamma-ray Space Telescope for which we can track the evolution of both the thermal and non-thermal emission on very short time scales. I will show why this combination of components is preferred over the other traditional models. In the context of the popular Fireball model, we estimated the magnetization of the outflow, the evolution of the jet Lorentz factor and photospheric radius, and the injection radius and energy.