MHD decomposition explains diffuse ?-ray emission in Cygnus X

Cosmic-ray (CR) diffusion is the result of the interaction of such charged particles against magnetic fluctuations. These fluctuations originate from large-scale turbulence cascading toward smaller spatial scales, decomposed into three different modes, as described by magnetohydrodynamics (MHD) theory. As a consequence, the description of particle diffusion strongly depends on the model describing the injected turbulence. Moreover, the amount of energy assigned to each of the three modes is, in general, not equally divided, which implies that diffusion properties might be different from one region to another. Here, motivated by the detection of different MHD modes inside the Cygnus-X star-forming region, we study the 3D transport of CRs injected by two prominent sources within a two-zone model that represents the distribution of the modes. Then, by convolving the propagated CR distribution with the neutral gas, we are able to explain the 7-ray diffuse emission in the region, observed by the Fermi-LAT and HAWC Collaborations. Such a result represents an important step in the long-standing problem of connecting the CR observables with the microphysics of particle transport.

Automated summary

The study discusses the mechanism of cosmic-ray diffusion, noting that the diffusion of particles is closely related to the description of injected turbulent models and that uneven energy distribution may lead to different diffusion characteristics in different regions. By tracking the three-dimensional transport of CR injected by two prominent sources, the authors explain the γ-ray diffuse radiation in the Cygnus-X region, observed by Fermi-LAT and HAWC Collaborations.