Demystifying the Prompt Emission of GRBs

Gamma Ray Bursts (GRBs) are the most energetic explosions in the Universe, producing up to ~10⁵³ ergs of energy in the first few seconds of their emission - the so-called prompt phase that is dominated by high energy X-ray and γ-ray photons. The very large luminosities released in these events make GRBs an ideal laboratory for exploring the interplay between matter and radiation under extreme conditions. The available GRB data has provided much insight on which models best explain observations, contributing to a general understanding of these events. However, there is still much more information hidden in the data. This information can shed light on the microphysical processes that are relevant to radiation from jets, the properties of both the GRB jet and the environment surrounding the jet, and how the jet imprints its signature on the resulting radiation. The Monte Carlo Radiation Transfer code (MCRaT) studies the interplay between matter and radiation by conducting radiative transfer calculations using the background of a realistic jet profile acquired from special relativistic hydrodynamic simulations (SRHD) of GRBs. MCRaT injects thermal photons into the jet and Compton scatters and propagates the photons through the outflow, taking their polarization into account. Using MCRaT we show that the radiation signatures from GRB SRHD simulations are able to reproduce the Yonetoku and Golenetskii observational relationships. Furthermore, we show that the expected polarization signatures are also in agreement with the observations made by the POLAR instrument. Our MCRaT simulations are additionally able to reproduce common features of observed GRB spectra. Due to the ability of MCRaT to conduct radiation transfer calculations using the background of a realistic jet profile, we are able to begin understanding the complex relationship between the progenitor material, the jet matter and the radiation signature. This work has resounding implications for understanding the GRB environment and properties through the detected electromagnetic signal.