Cosmic Tricks and Multiwavelength Treats: From Galactic PeVatrons to Solar Axions with Jooyun Woo

Do Galactic PeVatrons exist? Yes! In 2021, the Large High Altitude Air Shower Observatory (LHAASO) detected a dozen Galactic sources of ultra-high-energy (UHE; >100 TeV) gamma rays—the smoking gun of cosmic rays with PeV (10¹⁵ eV) energies. This discovery confirmed the long-postulated PeVatrons, the accelerators of the most energetic cosmic rays in our Galaxy. The number of PeVatrons has since grown to 43, shifting the focus from their existence to their nature: What are they, and how do they operate?

In this talk, I will present the past four years of my effort to answer these questions by combining X-ray and gamma-ray observations with physically motivated modeling. The credentials of traditional candidates (supernova remnants and pulsar wind nebulae) are tested, while the uncharted territory of “dark PeVatrons” is explored. I will highlight the dark horse of this pursuit—NuSTAR, the first focusing hard X-ray telescope—and how I am repurposing its timeless optics into a key component of the International Axion Observatory (IAXO), the next-generation axion helioscope experiment.

Sponsored by the McDonnell Center for the Space Sciences.