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Session 78 - Unique Objects and Gamma Bursts.
Oral session, Thursday, June 13
We report the observations of the X-ray lobes of W50 associated with the compact source SS433 known by its semi-relativistic two-sided jets. The eastern and western lobes were observed with the Position Sensitive Proportional Counter (PSPC) on board ROSAT. The lobes are symmetrically displaced east and west of SS433, starting at \sim 15^\prime, elongated along the axis of the jets, with an enhanced emission at \sim 35^\prime, and extending out to \sim 40^\prime. With ROSAT, we were able to detect diffuse emission from the eastern lobe even further out to \sim 1^o. This emission is coincident with the brightest radio filament which is thought to be the radio `hot spot' associated with the relativistic jets from SS433 interacting with the ambient medium. The spectrum from this region is soft, and is either described by a power law with a steep photon index (\Gamma \sim 4), or a thermal bremsstrahlung with a temperature kT \sim 0.5 keV. We also report the ASCA observations of the eastern lobe which was detected from \sim 15^\prime to \sim 40^\prime. We combine the ASCA data with the ROSAT data to get a wide coverage of the spectra in the 0.1 -- 10 keV energy range. The spectra show softening with increasing distance from SS433. Both thermal bremsstrahlung spectra with high temperatures (\sim 5 -- 30 keV) as well as power law spectra with hard photon index (\Gamma \sim 1.4 -- 2) give adequate fits. The fits are made better by adding a Gaussian line around 2 keV or by fitting with a broken power law, with the break occurring at \sim 2 -- 3 keV. We discuss the thermal versus non-thermal origin of the X-rays in correlation with the maps of W50 at other wavelengths. We also discuss the morphology of the lobes and derive some physical parameters for the jets based on the existing models of supersonic jets interacting with the surrounding medium and producing a region of `hot' shocked material.
Program listing for Thursday