Luminosity dependent changes of pulse profiles in the X-ray binary GX 1+4

J.G. Greenhill ,
D. Galloway ,
M.C. Storey

Physics Department, University of Tasmania, GPO Box 252C, Hobart, Tas 7001
John.Greenhill@utas.edu.au, Duncan.Galloway@utas.edu.au
Special Research Centre for Theoretical Astrophysics, School of Physics, University of Sydney, NSW 2006
michelle@physics.usyd.edu.au

Abstract:

We have reviewed the X-ray pulse profiles from a large number of observations of the accreting binary pulsar GX 1+4 obtained during the last 25 years. The profiles cover various energy ranges between 1 and 100 keV. Using these data we present a coherent picture of present and past pulse profiles and the variations of these pulse profiles with time. The pulse shape is dependent on both the X-ray luminosity and whether the pulsar is spinning up or down. Profiles measured during the GX 1+4 high state in the 1970's are all trailing edge bright. Subsequently the profiles have generally been symmetric or leading edge bright. Rossi X-ray Timing Explorer (RXTE) satellite data taken in July, 1996 show that similar pulse shape variations can occur on a timescale of hours. The implications of this new information for accretion models is discussed.

Keywords: X-rays:stars - accretion discs - pulsars:individual:GX 1+4

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