MULTIMISSION OBSERVATIONS OF 4U-1538-52

Archival data from the eclipsing binary X-ray pulsar 4U 1538-52 have been analyzed. These data were obtained from four different X-ray missions and span a baseline of 12 yr. Scanning observations were made using the Uhuru satellite during 1972 May 9-15 and using HEAO A1 during 1977 August 26-31 and 1978 February 22-28. Pointed observations were made using the Einstein Observatory during 1979 March 2 and EXOSAT during 1984 March 17, August 7-8 and 10-11. These data are used to improve the orbital period determination, to set a limit to the change in orbital period, and to improve the knowledge of the pulse period as a function of time. EXOSAT pulse profiles are presented and pulse-phase spectroscopy is performed. The pulsation observations of 4U 1538-52 are modeled geometrically and parameters for magnetic beaming of the accretion column are derived.