The evolving microphysics of particle acceleration and field generation in gamma-ray burst afterglow shocks

Daniel Groselj, Ph.D.

Despite decades of research on gamma-ray bursts (GRBs)—the most powerful cosmic explosions—the physical mechanisms behind their emission remain poorly understood. Recent discoveries, such as the brightest-ever GRB 221009A, or the electromagnetic counterpart of the gravitational-wave event GW170817, have reignited interest in this long-standing problem.
The prompt GRB emission, which typically lasts from a fraction to a few tens of seconds, is followed by a long-lasting afterglow from a relativistic collisionless shock that gradually expands into the ambient medium. During its lifetime, the afterglow shock covers different stages of evolution: a regime with strong radiative feedback during the first tens of minutes, a “pure” relativistic flavor on timescales of days and months, and the mildly relativistic regime at very late time.

Here, I will present recent kinetic studies of GRB shock physics that touch upon all stages of the shock evolution. I will discuss (1) how the shock physics is shaped by the electron-positron pair enrichment of the ambient medium during the early GRB afterglow, (2) the evolution of relativistic collisionless shocks on time scales beyond those accessible to previous simulations, and (3) the physics of particle acceleration and magnetic field generation in the mildly relativistic regime. I will also comment on the implications of these results for models of GRB afterglows.

To participate in this event virtually via Zoom, go to https://uiowa.zoom.us/j/91452787866?from=addon.