2025 Theses Doctoral

From photons to cosmic rays: a multiwavelength pursuit of Galactic PeVatrons

Woo, Jooyun

The origin of cosmic rays has been a century-long outstanding question. In particular, the accelerators of the most energetic cosmic rays in our galaxy, “Galactic PeVatrons”, have drawn great attention in the community for understanding an extreme cosmic-ray acceleration mechanism and other closely related processes such as diffusion and cooling.

The most energetic cosmic rays emit TeV gamma rays and hard X-rays, whose spatial and energy distribution deliver crucial information about the cosmic rays and the astrophysical environment in which the cosmic rays are accelerated. Since different information is delivered in different energies of photons, one needs to observe a cosmic-ray source with multiwavelength instruments to obtain a complete view of physical processes in the cosmic-ray source.

This work presents X-ray and gamma-ray observations of three Galactic PeVatron candidates – a young supernova remnant Cassiopeia A, a middle-aged pulsar wind nebula Dragonfly, and a halo around an old pulsar LHAASO J0621+3755. Each candidate is examined for its capability of cosmic-ray acceleration, and investigated for its unique insight into different cosmic-ray processes. Prospects for identifying Galactic PeVatrons are discussed.