Two-zone diffusion of electrons and positrons from Geminga explains the positron anomaly

Understand

The recent HAWC observations of very-high-energy $\gamma$-ray halo around Geminga and Monogem indicate a very slow diffusion of cosmic rays, which results in tiny contribution of positrons from these two pulsars to the local flux.

• This makes the cosmic positron excess anomaly observed by PAMELA and AMS-02 even more puzzling.
• However, from the Boron-to-Carbon ratio data one can infer that the average diffusion coefficient in the Galaxy should be much larger.
• In this work we propose a two-zone diffusion model that the diffusion is slow only in a small region around the source, outside of which the propagation is as fast as usual.