X-RAY OBSERVATIONS OF THE SLOWEST KNOWN BE X-RAY PULSARS RX-J0146.9+6121 AND X-PERSEI/

We present ASCA and ROSAT observations of the Be/X-ray binary pulsars RX J0146.9+6121 and X Persei between 1994 and 1996. Measuring the neut ron star spin period and X-ray luminosity of X Persei shows that the e pisode of low X-ray luminosity and monotonic spin-down since 1978 cont inued to at least August 1995. ASCA and ROSAT HRI observations of RX J 0146.9+6121 detected the pulsar with the longest known neutron star sp in period at low luminosities after the X-ray outburst seen by EXOSAT in August 1984. The large spin period decrease seen between 1984 and 1 993 has nearly stopped at a period of 1407.3 s in February 1996. We di scuss that the X-ray outburst behaviour of X Persei with respect to it s Be star phase changes observed in the optical can be caused by an as ymmetry in the matter distribution around the Be star.