High-Energy Studies of Galactic Cosmic Ray Accelerators

The Milky Way Galaxy is rich with Galactic cosmic ray (CR) accelerators such as the remains of massive stellar explosions, supernova remnants (SNRs). In the center of many core collapse SNRs are highly magnetized, rapidly rotating compact stellar cores known as pulsars. Energetic pulsars may form a pulsar wind nebula (PWN) through the conversion of rotational energy into a strongly magnetized, relativistic particle outflow. PWNe make up most of the very high energy (VHE, E > 100GeV) Galactic source population detected by Imaging Air Cherenkov Telescopes (IACTs). Gamma-ray PWNe are strong CR accelerator candidates since gamma-rays are produced via CR interactions, specifically the relativistic electrons of the PWN Inverse Compton Scatter off lower-energy photons. As such, PWNe may be responsible for producing Galactic CRs with energy up to ~ 1PeV. The Fermi-LAT is the most sensitive instrument observing the lower-energy (E < 100GeV) gamma-ray sky, where many PWNe are expected to peak. Fermi-LAT observations can provide important constraints on the acceleration mechanisms and thus the ability for a source to contribute to the Galactic CR flux. Recent results analyzing coincident Fermi-LAT gamma-ray emission to known PWNe and the physical implications are presented. A systematic search suggests that a larger population of Fermi-LAT PWNe than currently identified exists with many found as extended and in later stages of evolution which can be studied in greater detail using broadband studies.