Rossi X-Ray Timing Explorer Observations of the Eastern Lobe of W50 Associated with SS 433

We present the Rossi X-Ray Timing Explorer (RXTE) observations of the SNR W50, associated with SS 433. The observations cover the X-ray lobe found between SS 433 and the outer eastern radio ``ear'' of W50. The X-ray spectrum measured with the proportional counter array and the High-Energy Timing Experiment in the 3-100 keV range favors nonthermal over thermal models for this part of W50. We combine the RXTE spectrum with the ROSAT and ASCA spectra, thus covering ~3 orders of magnitude in energy. The spectrum of the harder X-ray emission is well represented by a power law with a photon index of ~1.45 and a total X-ray luminosity of ~1.5×10³⁵ ergs s^-1 for a source distance of 5.5 kpc. We thus confirm the nonthermal nature of the inner X-ray lobe. We discuss its implications in the context of the interaction between the jets from SS 433 and the surroundings.