LUMINOSITY DEPENDENT CHANGES OF PULSE PROFILES IN THE X-RAY BINARY GX-1+4

We have reviewed the X-ray pulse profiles from a large number of obser vations of the accreting binary pulsar GX 1 + 4 obtained during the la st 25 years. The profiles cover various energy ranges between 1 and 10 0 keV. Using these data we present a coherent picture of present and p ast pulse profiles and the variations of these pulse profiles with tim e. The pulse shape is dependent on both the X-ray luminosity and wheth er the pulsar is spinning up or down. Profiles measured during the GX 1 + 4 high state in the 1970s are all trailing edge bright. Subsequent ly the profiles have generally been symmetric or leading edge bright. Rossi X-ray Timing Explorer (RXTE) satellite data taken in July 1996 s how that similar pulse shape variations can occur on a timescale of ho urs. The implications of this new information for accretion models is discussed.