******************************************************
   PR # 21064
    We propose to observe the west lobe of W50,a supernova remnant contai
    ning SS 433 at its center.The two X-ray lobes are located symmetrical
    ly with respect to SS 433,corresponding to the "ears" of the SNR shel
    l in the radio map.They are considered to be produced by the collisio
    n of the jet with the interstellar matter such as the SNR shell. The 
    west lobe is located nearer to the galactic plane, and is supposed to
    interact with denser matter than the east lobe.  The east lobe was ob
    served by ASCA in PV phase.  Contrary to the general expectation, its
    spectrum was found to be non-thermal. The comparison of the two lobes
    should lead us to understand the emission mechanism by controlling   
    small number of parameters: i.e. same energy input, same history, and
   different matter density.     
 ******************************************************