E. Lammert | Searcharxiv

arXiv2026

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

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.

astro-ph.HE↗

arXiv2025

Cygnus X-3 as semi-hidden PeVatron

The high-mass X-ray binary Cygnus X-3 has been suggested for a long time to be a source of high-energy photons and neutrinos. In view of the increased sensitivity of current experiments, we examine the acceleration and interactions of high-energy cosmic rays (CRs) in this binary system, assuming that the compact object is a black hole. Using a test-particle approach in a Monte-Carlo framework, we employ as the basic CR acceleration mechanisms magnetic reconnection or second-order Fermi and diffusive shock acceleration. We find that in all three scenarios CRs can be accelerated beyond PeV energies. High-energy photons and neutrinos are produced as secondaries in photo-hadronic interactions of CRs on X-ray photons and in the scattering on gas from the wind of the companion star. Normalising the predicted photon flux to the excess flux observed by LHAASO at energies above PeV in the direction of Cygnus X-3, a CR acceleration efficiency of $10^{-3}$ is sufficient to power the required CR luminosity. Our results suggest that the PeV photon flux from Cygnus X-3 could be in a bright phase significantly increased relative to the average flux of the last years.

astro-ph.HE↗