Deciphering the Origin of the GeV--TeV Gamma-ray Emission from SS 433.

We investigate hadronic and leptonic models for the GeV--TeV gamma-ray emission from jets of the microquasar SS 433. The emission region of the TeV photons coincides with the X-ray knots, where electrons are efficiently accelerated. On the other hand, the optical high-density filaments are also located close to the X-ray knots, which may support a hadronic scenario. We calculate multi-wavelength photon spectra of the extended jet region by solving the transport equations for the electrons and protons. We find that both hadronic and leptonic models can account for the observational data, including the latest {\it Fermi} LAT result. The hadronic scenario predicts higher-energy photons than the leptonic models, and future observations such as the Cherenkov Telescope Array (CTA), the Large High-Altitude Air Shower Observatory (LHAASO), and the Southern Wide-field Gamma-ray Observatory (SWGO) may distinguish between these models and unravel the emission mechanism of GeV--TeV gamma-rays. Based on our hadronic secenario, the analogy between microquasars and radio galaxies implies that the X-ray knot region of the jets in radio galaxies may accelerate heavy nuclei up to ultrahigh energies.