Cosmic-Ray Propagation in Light of the Recent Observation of Geminga

• Published in: The Astrophysical journal Vol. 879; no. 2; pp. 91 - 103
• Main Authors: Jóhannesson, Gu laugur, Porter, Troy A., Moskalenko, Igor V.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 10.07.2019; IOP Publishing
• Subjects: astroparticle physics; Astrophysics; Cosmic ray propagation; cosmic rays; Diffusion; Diffusion models; Diffusion rate; Emission; Galaxy: structure; Gamma emission; gamma rays: diffuse background; gamma rays: ISM; High altitude; Interstellar matter; Interstellar medium; Mathematical models; Milky Way; Nebulae; Propagation; Pulsar winds; Pulsars; Species diffusion; Stellar winds; gamma rays: diffuse background; diffusion; Galaxy: structure; cosmic rays; gamma rays: ISM; astroparticle physics
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/ab258e

The High Altitude Water Cherenkov (HAWC) telescope recently observed extended emission around the Geminga and PSR B0656+14 pulsar wind nebulae (PWNe). These observations have been used to estimate cosmic-ray (CR) diffusion coefficients near the PWNe that appear to be more than two orders of magnitude smaller than the diffusion coefficients typically derived for the interstellar medium from measured abundances of secondary species in CRs. Two-zone diffusion models have been proposed as a solution to this discrepancy, where the slower diffusion zone (SDZ) is confined to a small region around the PWN. Such models are shown to successfully reproduce the HAWC observations of the Geminga PWN while retaining consistency with other CR data. It is found that the size of the SDZ influences the predicted positron flux and the spectral shape of the extended γ-ray emission at lower energies that can be observed with the Fermi Large Area Telescope. If the two observed PWNe are not unique, then it is likely that there are similar pockets of slow diffusion around many CR sources elsewhere in the Milky Way. The consequences of such a picture for Galactic CR propagation is explored.