Demystifying the Prompt Emission of Gamma Ray Bursts

A full understanding of Gamma Ray Bursts (GRBs) is inhibited by the unknown radiative mechanisms that produce their observed prompt emission. Understanding the physics at play in producing the prompt emission can shed light on the structure of GRB jets and their central engines. Many past GRB prompt emission studies make assumptions about the radiation that is trapped within the jet or about the temporal and spatial structure of the jet, which limit their predictability. To circumvent these assumptions, we have developed the MCRaT radiative transfer code which allows us to simulate the radiation evolving within the structure of a hydrodynamically simulated GRB jet. The code simulates GRB prompt emission from optical to gamma-ray energies by taking Compton scattering, including the full polarized Klein–Nishina cross section, and cyclo-synchrotron emission and absorption into account. This capability allows us to make time integrated and time resolved predictions based on the structure of the hydrodynamically simulated jet. These predictions can be compared to observations and used to refine our understanding of the radiative mechanisms at play in GRBs. Additionally, we can investigate where photons of various energies originate from within a given GRB jet. We find that gamma-ray photons probe the structure of the GRB jet along the observers line of light while optical photons probe dense regions of the jet, either at shock fronts or the cocoon region. Interpreting multiwavelength observations of GRB prompt emission using our simulations can provide valuable insight into the structure of GRB jets.