CCAPP Seminar: Siddhartha Gupta (Princeton)

Energetic charged particles, known as cosmic rays, are the primary contributors to the nonthermal energy budget in the universe. Cosmic rays are mostly accelerated in collisionless shocks, which are ubiquitous in astrophysical environments and are also studied in laboratory experiments. While the primary acceleration mechanism---diffusive shock acceleration---is well established, the processes responsible for the injection of thermal electrons into diffusive shock acceleration and energizing them into the nonthermal energy state remain poorly understood.

 

In this talk, I will discuss our recent efforts to address this challenge using first-principles kinetic plasma simulations of non-relativistic shocks. I will emphasize the critical role of self-generated plasma instabilities in both the injection and the enhancement of the energy of nonthermal particles. This study is essential for developing subgrid prescriptions for nonthermal processes. Finally, I will demonstrate how subgrid models derived from kinetic simulations can be applied to interpret the phenomenology of nonthermal radio, X-ray, and gamma-ray emission from astrophysical sources.