Near-periodical spin period evolution in the binary system LMC X-4

In this paper, we investigated the long-term evolution of the pulse period in the high-mass X-ray binary LMC X-4 by taking advantage of more than 43 yr of measurements in the X-ray domain. Our analysis revealed for the first time that the source is displaying near-periodical variations of its spin period on a time-scale of roughly 6.8 yr, making LMC X-4 one of the known binary systems showing remarkable long-term spin torque reversals. We discuss different scenarios to interpret the origin of these torque reversals.