Fermi on the Origin of Galactic Cosmic Rays
To resolve the origin of Galactic cosmic rays, a chief difficulty has been to identify active accelerators and measure the energetics of protons and electrons. Seven years ago, the launch of Fermi promised to reveal a new population of gamma-ray supernova remnants (SNRs) and determine their energetics. Now we have clear evidence that cosmic-ray protons are accelerated in at least some SNRs and a population of more than 30 gamma-ray SNRs in which to trace the acceleration, escape, and diffusion of cosmic rays. The Fermi LAT team recently released a new event-level analysis, dubbed Pass 8, which delivers dramatically improved spatial resolution and sensitivity at the lowest and highest energies. I present new morphological and spectral analyses of individual SNRs, as well as blind surveys for Galactic gamma-ray sources, that are bringing us ever closer to solving the cosmic-ray mystery.