Prof. Andrzej Zdziarski

Cyg X-3 is a unique X-ray binary. In particular, it is a powerful source of orbitally modulated gamma-rays at GeV energies, emitted by its jets. Recently, the LHAASO collaboration discovered PeV photons from Cyg X-3. Two of them have energies >3 PeV (>5000 erg), the highest ever detected from an astrophysical source. I will discuss a model that explains the LHAASO results. PeV-range photons are produced when hadrons with energies up to >10 PeV interact with both the blackbody photons and the stellar wind emitted by the donor, producing neutral pions that subsequently decay into gamma-rays. Given the very low cross sections for these processes and the low inclination of the source, hadrons accelerated by the counterjet toward the observer dominate the observed emission, opposite to the usual jet dominance.