ORBITAL DECAY IN THE X-RAY BINARY LMC-X-4

We report on the timing analysis of the high-mass X-ray binary (HMXRB) LMC X-4 with the ROSAT satellite. The observation covers about three binary orbits in the high-intensity state of the 30 day cycle of LMC X -4, thus allowing an accurate determination of the pulse period and th e orbital parameters of the 13.5 s X-ray pulsar. The new mid-eclipse e poch, combined with the previous epochs, suggests orbital decay in LMC X-4 at a rate of P-orb/P-orb similar to -5 x 10(-7) yr(-1). An interp retation of our results is discussed in the context of conservative ma ss loss and tidal evolution and in comparison with the other HMXRB Cen X-3.