A pulse timing study of the X-ray pulsar 4U 1145-619.

Abstract

EXOSAT observations of the X-ray pulsar 4U1145-619, which is known to exhibit X-ray outbursts on an apparently regular 187-day cycle, have revealed a rapid decrease in the pulse period during the outburst states, whereas on longer time-scales the pulse period is found to be stable. The X-ray luminosity is too low, even during outburst, to account for this phenomenon in terms of spin-up and spin-down rates arising from mass accretion on to the neutron star. It is shown, however, that orbital motion could generate the observed pulse period variations if the orbital eccentricity of the system is at least 0.6.