A dual-zone diffusion model for high energy emissions of the Cygnus Cocoon

Abstract

ABSTRACT As one of the brightest Galactic γ-ray sources, the Cygnus Cocoon superbubble has been observed by many detectors, such as Fermi-LAT, ARGO, HAWC, and LHAASO. However, the origin of γ-ray emission for the Cygnus Cocoon and the possible contribution to PeV cosmic rays are still under debate. The recent ultrahigh-energy γ-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 γ-ray data from GeV to ∼50 TeV and agree with the one sub-PeV neutrino event result from IceCube so far. Moreover, it predicts a non-negligible contribution γ-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.