Gamma-ray bursts (GRBs) are an extreme variety of cosmic explosion and perhaps the most powerful events yet discovered. After a lot of work, GRBs are now known to be at large distances, significant fractions of the size of the universe. They come from very high speed jets of material shot out by short-lived compact sources, possibly during the formation of black holes. At least in some cases, GRBs are associated with the collapse of very massive stars of the type called Wolf-Rayet. This work should make transformative progress on a major goal of GRB theory, which is to use available observations all the way from low energies (long wavelengths, radio data) to the highest energies (short wavelength, gamma rays), to reconstruct the explosion, determining the composition of the jets, how they are made, how they emit gamma rays, and how they interact with their surroundings. Junior researchers at the beginning of their careers will learn about complex theories and computer simulations and contribute to the understanding of fundamental physics and the properties of matter in extreme conditions.
This research will revisit the mechanism of shocks in GRBs, and analyze their radiative properties. It will use ab initio numerical simulations to investigate a new type of sub-photospheric shock. By following shock formation and propagation on a microscopic level, these simulations will fully describe the dissipation mechanism and the radiation produced. These results will then be tested against observations. The study includes work on a mechanism for the observed GeV flashes in GRBs which has already raised new questions about the physics of the external blast waves from GRB explosions, and in particular suggests the possibility of a non-linear shock which has a strong precursor and involves ultra-high-energy electron-positron pairs. Both the simulation method and the shock mechanism are novel and could potentially uncover unexpected features in the blast wave mechanism. The research impacts fundamental physics by understanding new properties of matter in extreme conditions. Educational impacts include the training of junior researchers and incorporation of results into instructional courses.
