Improving and Extending Models of Gamma-Ray Burst Afterglows

Gamma-ray bursts (GRBs) are the most luminous cosmic explosions. They are some of the more extreme objects in the Universe, both mysterious and fascinating. Understanding their origin and development provides insights into star formation and evolution, as well as tests of basic physics. The afterglow left after a GRB goes off is due to interactions in the material around the explosion and can be observed long after the initial blast. This project will probe the afterglow phase in new ways using extensive computer simulations to go beyond the simple models and explain otherwise puzzling recent observations.

Because of the way the spectrum of the afterglow changes with time, the dominant emission mechanism was thought to be synchrotron radiation from shock-accelerated electrons. However, the detection of photons with energies that violate the maximum synchrotron limit shows that theoretical understanding of the afterglow emission is still incomplete. Current models have little predictive power due to ignorance of the underlying microphysics. This work will go beyond standard phenomenological approaches, building on recent results by this research team that have started to unveil the microphysics of GRB afterglows. Self-consistent particle-in-cell simulations will provide physically grounded microphysical parameters at every stage. This study will (1) settle the question of the origin of the magnetization; (2) study the shock physics in early GRB afterglows, investigating the electron-positron-proton plasma shocks; and (3) explore the shock physics in late GRB afterglows. The research will assess the efficiencies of electron and proton acceleration in late GRB shocks, and the decay length of the generated and amplified fields.

Despite the complex physics involved, this work contains several projects for undergraduate students, and even high school students can be exposed to the latest developments about relativistic shocks through day-long workshops. The team is committed to significant involvement with established educational and mentorship programs, including support for children and adolescents from disadvantaged neighborhoods.