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    PR # 31051                                                                   
     We propose to monitor the highly eccentric Be/radio pulsar binary PSR       
      B1259-63 with ASCA in a series of two 20ks observations as the pulsa       
     r approaches its apoastron. The binary system includes the key proces       
     s of X-ray emission by the shock waves in the interaction region betw       
     een the relativistic pulsar wind and the Be star mass outflow. By con       
     traries to the standard model of the shock excitation, results from p       
     receding ASCA observations revealed that X-ray flux at about 90 degre       
     e from periastron increased by about 2 factors of magnitude than that       
      at periastron. The series of proposed ASCA observations will give us       
      an important clue to understand the nature of the interaction betwee       
     n the pulsar and Be stellar wind as well as the structure and origin        
    of the Be stellar wind.                                                      
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