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~yrs 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~yrs, 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. 
S. Molkov, A. Lutovinov, M. Falanga, S. Tsygankov and E. Bozzo
astro-ph.HE