MAGNETIC RECONNECTION AND ENERGETICS IN THE RELATIVISTIC JETS OF GAMMA-RAY BURSTS

Gamma-ray bursts (GRBs) are among the most powerful and enigmatic phenomena in our universe. They are short, irregular, and highly energetic bursts originating from distant regions of space. These bursts are typically classified as short, or long, typically associated with binary neutron star mergers and the core collapse of massive stars, respectively, and have two main distinguishable features: the prompt emission, where most of the gamma-rays are produced in a matter of seconds, and the afterglow, where emission in longer wavelengths (X-rays, visible light, radio) can be observed for years after the burst. Significant progress in observations, theoretical modeling, and simulations has helped us understand the after-glow emission rather well. However, key questions remain about the nature of the central engines and the mechanisms that power the gamma-ray emission. This PhD thesis presents three distinct yet interconnected theoretical projects aimed at addressing some of these key questions surrounding GRB central engines and the behavior of their relativistic jets. By employing a range of analytical, computational, and data-driven techniques, these projects seek to enhance our understanding of the microphysical processes and macroscopic dynamics that govern these powerful astrophysical explosions.

The first project investigates the connection between the early afterglow and the prompt emission of GRBs within the context of the striped jet model. By using afterglow observations of the jet’s bulk Lorenz factor and magnetization at large distances, we test the striped jet model for the GRB flow and study its predictions for the prompt emission and the constraints on the nature of the central engine. The second project introduces a unified theoretical framework for GRB central engines, encompassing both standard thin accretion disks and magnetically arrested disks (MADs). This model focuses on the Blandford-Znajek (BZ) mechanism as the primary engine for launching GRB jets, where the rotational energy of a central black hole is extracted via the magnetic fields that thread it. The third project utilizes high-resolution Particle-in-Cell (PIC) simulations to investigate the triggering of magnetic reconnection under the effects of expansion in the acceleration phases of highly magnetized jets.