A Dual-Zone Diffusion Model for High Energy Emissions of the Cygnus Cocoon

Abstract

As one of the brightest galactic ${\gamma}$-ray sources, the Cygnus Cocoon superbubble has been observed by many detectors, such as $Fermi$-LAT, ARGO, HAWC, and LHAASO. However, the origin of $\gamma$-ray emission for the Cygnus Cocoon and the possible contribution to PeV cosmic rays are still under debate. The recent ultrahigh-energy $\gamma$-ray observations by LHAASO up to 1.4 PeV towards the direction of the Cygnus Cocoon, as well as the neutrino event report of IceCube-201120A coming from the same direction, suggest that the Cygnus Cocoon may be one of the sources of high-energy cosmic rays in the Galaxy. In this work, we propose a dual-zone diffusion model for the Cygnus Cocoon: the cocoon region and surrounding interstellar medium (ISM). This scenario can account for the $\gamma$-ray data from GeV to $\sim$ 50 TeV and agree with the one sub-PeV neutrino event result from IceCube so far. Moreover, it predict a non-negligible contribution $\gamma$-ray emission at hundreds TeV from the ISM surrounding the Cygnus Cocoon. This possible diffuse TeV-PeV gamma-ray features can be resolved by the future LHAASO observations.