Slow diffusion around pulsar $\gamma$-ray halos and its impact on cosmic rays propagation

TL;DR

This paper demonstrates that slow diffusion around pulsar gamma-ray halos is essential for accurately modeling cosmic ray propagation and reassesses the contributions of pulsars and dark matter to positron fluxes in light of this slow diffusion.

Contribution

It shows that ballistic-diffusive propagation cannot explain gamma-ray halos and emphasizes the necessity of slow diffusion in cosmic ray models, impacting interpretations of AMS-02 data.

Findings

Slow diffusion is necessary to explain gamma-ray halos.

Dark matter annihilation remains consistent with gamma-ray limits under the new model.

Positron flux from pulsars is affected by slow diffusion considerations.

Abstract

The diffusion coefficients around the pulsar $\gamma$-ray halos are highly suppressed compared with the value in the interstellar medium. It is suggested in the literature that the $\gamma$-ray halos can be explained by a ballistic-diffusive (BD) propagation without slow diffusion. However our calculation shows that the BD propagation can not account for the $\gamma$-ray halo profile well. Furthermore the transfer efficiency of the pulsar spin down energy to the high energy electrons and positrons is even larger than 1 in the BD scenario. Therefore slow diffusion is necessary to account for the pulsar $\gamma$-ray halos. Taking the slow diffusion into account the contribution of positron flux originated from nearby pulsars to the AMS-02 data is reexamined. We may also expect a slow diffusion disk of the Milky Way as many such slow diffusion regions exist. The positron contribution to the AMS-02 data from dark matter annihilation in the new propagation model is also reexamined. We find that the dark matter scenario satisfies all the $\gamma$-ray limits in the new propagation model.