Speaker
Description
Recently, massive-star environments have been established as a new class of gamma-ray sources, which can show degree-scale diffuse emission up to ultra-high energies. They are shaped by feedback from massive stars and harbour a variety of particle accelerators, such as supernova remnants, stellar-wind shocks, and compact objects. A concerted effort of both detailed gamma-ray analyses and physical modelling of these environments is necessary to pin-point acceleration sites and assess the role of massive-star environments in the Galactic cosmic-ray ecosystem, regarding the origin of PeV cosmic rays and Galactic particle transport. In this talk, I present our recent efforts in both gamma-ray modelling and 3D (M)HD simulations of massive-star environments. In particular, I demonstrate that a tens-of-kyr old, powerful supernova expanding rapidly in a low-density superbubble can account for the recent detection of PeV photons from the Cygnus region (Härer+ 25b, accepted). We fit the broadband gamma-ray spectrum and morphology with a lepto-hadronic model, which includes the above mentioned supernova (hadronic emission, 10 TeV-PeV) and stellar-wind shocks (leptonic emission, GeV-TeV). I discuss these results in the context of background from Galactic diffuse emission and other source candidates. To recover the energy dependence of the morphology, we construct a 3D molecular cloud model and solve the transport equation to obtain the radial particle distribution. We estimate the supernova maximum energy from dedicated a 3D HD simulation of the stellar association Cygnus OB2 (Vieu et al. 2024). I emphasise how we use 3D HD and MHD simulations to constrain ambient conditions in massive-star environments more generally. For example, we demonstrated in Härer+ 25a that stellar-wind interaction results in highly non-trivial magnetic field morphologies and non-uniform shocks, which can result in steep, curved spectra, as typically observed from massive-star environments.
