Multimission observations of 4U 1538 - 52

Abstract

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 May 9-15, 1972 and using HEAO A1 during August 26-31, 1977 and February 22-28, 1978. Pointed observations were made using the Einstein Observatory during March 2, 1979 and Exosat during March 17, August 7-8 and 10-11, 1984. 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.