SOME CHARACTERISTICS OF TIMING AND ENERGY SPECTRUM OF X-RAY PULSAR 4U 1538-52

The source 4U 1538--52 is one of the well-studied X-ray pulsars. 4 mediumenergy (ME) observations with EXOSATare processed and analyzed, in which 2observations are during the X-ray eclipsing. Combined with the results of the otherobservations, some analyses and explainations are given in this paper. The spin-downof the neutron star is continuing duering the observations. The energy spectrum isthe power law spectrum, the iron line is not seen after Tenma observations. It isassumed that the X-ray dips will occur when the neutron star is eclipsed by a foreground star, a late-type dwarf. The X-ray bursts which sustained about 1 hour areformed by the increasing mass exchange and could occur at the different orbit phase.And there seem to be an emission line at the energy near 1 keV, if it is a cyclotronline, the magnetic field of the surface of the neutron star would be 8.6(1 + z) × 10⁶T.