ROSAT and ASCA Observations of W50 Associated with the Peculiar Source SS 433

Abstract

We report the observations of the X-ray lobes of the large Galactic source W50 associated with the two-sided jets source SS 433. The observations were made with the Position Sensitive Proportional Counter on board ROSAT. The eastern lobe has a knotty structure, with X-ray emission starting at D15@ from SS 433 and peaking at D35@. Both thermal bremsstrahlung spectra with high temperatures (º5 keV), as well as power-law spectra with Ñat photon index (! D 1È2), gave adequate Ðts. With ROSAT , we also detected an additional soft X-ray emission from the eastern lobe, at D1¡ east of SS 433 and coincident with the radio "" ear.ÏÏ This region is associated with the terminal shock of the SS 433 jets. The western lobe has a similar morphology ; however, the spectrum is softer, and no emission was found coincident with the western radio "" ear.ÏÏ We also report the observations of W50 with the Advanced Satellite for Cosmology and Astrophysics (ASCA), and combine the ROSAT and the ASCA data for a wide coverage of the spectra in the 0.1È10 keV energy range. We Ðnd that the spectrum from the brightest region (at D35@ from SS 433) requires an additional component to account for an excess of photons in the 1È3 keV band. The total X-ray luminosity from both lobes is ergs s~1. D1035È1036D 5.5 2 We discuss the origin of the X-rays in the model of emission from the supersonic jets of SS 433 interacting with the ambient medium, accelerating particles to very high energies, and producing a cocoon of "" hot ÏÏ shocked material. We present our interpretation in light of the correlation of X-ray emission with the map of W50 at other wavelengths.