Discovery of CO Clouds Associated with the X-Ray Jets of SS 433: Evidence for Shock–Cloud Interaction Enhancing Nonthermal X-Ray Emission

We report the first identification of molecular clumps directly associated with the rebrightening regions of the large-scale X-ray jets of SS 433, based on 12 CO ( J = 1–0) observations with the Nobeyama 45 m Radio Telescope. Multiple clumps are detected toward the eastern and western jet heads, showing clear spatial correlation with the X-ray emission. The X-ray emission peaks immediately downstream of the molecular clumps, while the hardness ratio is enhanced at their surfaces, indicating that the observed structures cannot be explained by absorption effects. These results provide direct evidence for shock–cloud interactions between the jets and the surrounding interstellar medium. We suggest that turbulence generated at the jet–cloud interface amplifies magnetic fields, producing the observed nonthermal X-ray emission. Our findings highlight the importance of jet–interstellar medium interactions in shaping the X-ray properties of microquasar jets.