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

TL;DR

This paper discusses how Cygnus X-3 can accelerate cosmic rays beyond PeV energies, with recent observations from LHAASO supporting the idea of jet-based acceleration and photon flux modulation due to stellar wind interactions.

Contribution

It extends previous work by linking LHAASO observations to cosmic ray acceleration in Cygnus X-3's jet and photon flux modulation mechanisms.

Findings

LHAASO detected orbitally modulated photons up to 4 PeV from Cygnus X-3.

Photon flux drops below PeV energies, likely due to absorption in stellar wind.

Cosmic ray acceleration occurs in the jet, with secondary production in wind and stellar UV photons.

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 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.