Discovery of a 30.5 day periodicity in LMC X-4

Observations covering a 500/sup d/ time span made with High-Energy X-ray and Low-Energy Gamma-Ray Instrument on HEAO 1 reveal a 30./sup d/48 +- 0./sup d/06 peroidic variability in the approx.13 to approx.80 keV flux from LMC X-4. The source intensity is modulated by at least a factor of 5 through the 30./sup d/5 cycle and is low for approx.40% of the cycle. A value of the orbital period P = 1./sup d/40839 +- 0./sup d/00010 is determined from the observations. Possible origins of the 30./sup d/5 period are discussed.