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 W 50, associated with SS 433. The observations cover the X-ray lobe found bet ween SS 433 and the outer eastern radio "ear" of W50. The X-ray spectrum me asured with the proportional counter array and the High-Energy Timing Exper iment 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 similar to 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 similar to 1.45 and a total X-ray luminosity of similar to 1.5 x 1 0(35) ergs s(-1) for a source distance of 5.5 kpc. We thus confirm the nont hermal nature of the inner X-ray lobe. We discuss its implications in the c ontext of the interaction between the jets from SS 433 and the surroundings .