Addendum to "Cygnus~X-3 as a semi-hidden PeVatron'' discussing the LHAASO 2025 data

Abstract

In a recent work, we have 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. 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.

Figures (3)

• Figure 1: The average photon flux as function of energy compared to the LHAASO data LHAASO from Cygnus X-3 in the flaring state (corrected for Galactic absorption); shown is also separately the contribution from scatterings on UV photons and gas.
• Figure 2: The energy gain rates for shock acceleration assuming Bohm and Kraichnan diffusion, as well as the energy loss rates due to synchrotron radiation and photo-hadronic interaction of stellar UV photons as funtion of the proton energy.
• Figure 3: The modulation amplitude of the photon flux produced in photo-hadronic interactions as function of the orbital phase.