Hunting Pulsar Wind Nebulae with the Fermi-LAT

Pulsar wind nebulae (PWNe), found in core collapse supernova remnants (SNRs), are some of the brightest and most energetic sources detected in the Milky Way Galaxy. These objects make up the majority of very high energy (VHE) sources detected by Imaging Air Cherenkov Telescopes (IACTs) such as HESS. The VHE emission is attributed to relativistic particles from the PWN Inverse Compton Scattering off of local photon fields, and is often accompanied by prominent X-ray emission from interactions with the PWN magnetic fields. As such, PWNe provide a direct view to some of the most extreme Galactic environments, which may be responsible for the production of particles to cosmic ray (CR) energies. The majority of PWNe have been discovered in radio or X-ray bands with an increasing number of PWN discoveries in the Cherenkov Telescope era, but only a handful of PWNe have been identified by the Fermi-LAT in the MeV—GeV band. PWNe are typically located along the Galactic plane, embedded within the bright diffuse gamma-ray emission, making identification with the Fermi-LAT difficult. Bright GeV emission from a central pulsar can also obscure PWNe. Taking advantage of the latest event reconstruction update for Fermi (Pass 8), I am performing a systematic search for gamma-ray emitting PWNe using 11.5 years of Fermi-LAT data, targeting the locations of known PWNe identified in other wavelengths. A second approach searches for new PWNe by selecting the off-pulse phases of Fermi-detected pulsars. The observational study will also consider available multi-wavelength data to be used in semi-analytic models that investigate the PWN morphology, particle injection spectrum, its evolution, and the overall nature of the particles which are eventually injected into the ISM and may be replenishing the Galactic CR population.