Measuring the Local Diffusion Coefficient with H.E.S.S. Observations of
  Very High-Energy Electrons
  The HAWC Collaboration has recently reported the detection of bright and
spatially extended multi-TeV gamma-ray emission from Geminga, Monogem, and a
handful of other nearby, middle-aged pulsars. The angular profile of the
emission observed from these pulsars is surprising, in that it implies that
cosmic-ray diffusion is significantly inhibited within ~25 pc of these objects,
compared to the expectations of standard Galactic diffusion models. This raises
the important question of whether the diffusion coefficient in the local
interstellar medium is also low, or whether it is instead better fit by the
mean Galactic value. Here, we utilize recent observations of the cosmic-ray
electron spectrum (extending up to ~20 TeV) by the H.E.S.S. Collaboration to
show that the local diffusion coefficient cannot be as low as it is in the
regions surrounding Geminga and Monogem. Instead, we conclude that cosmic rays
efficiently diffuse through the bulk of the local interstellar medium. Among
other implications, this further supports the conclusion that pulsars
significantly contribute to the observed positron excess.
