Cygnus X-3 as a PeVatron and the LHAASO 2025 data

Abstract

We have recently argued that the high-mass X-ray binary Cygnus X-3 can accelerate cosmic rays (CR) beyond PeV energies. Meanwhile, the LHAASO collaboration published the measurement of an orbitally modulated photon flux from Cygnus X-3 extending up to 4 PeV. In this short extension of our previous work, we argue that these observations point towards CR acceleration in the jet, and secondary production in CRs scattering on gas from the wind and on stellar UV photons from the companion star. The latter channel leads naturally to a contribution to the photon flux peaking around PeV energies which is strongly orbitally modulated. The fast drop in the flux of these photons below PeV energies may be caused by absorption on an increased density of background photons in a line-driven stellar wind.