Long-Term Observations of Cygnus X-3 with VELA 5B

The authors present long-term (1969 - 1979) observations of Cygnus X-3, obtained by the Vela 5B satellite at 3 - 12 keV, with 10^d time resolution. The object has a 4.8 hr period which is thought to be orbital. Long-term periodicities of 17^d, 20^d, and 33^d - 34^d have been reported by several authors. The authors of this paper do not observe the 17^d and 33^d - 34^d variations, and set upper limits significantly lower than the reported amplitude of the 33^d - 34^d variation. The 4.8 hr variation is evident in the data, appearing with the doubly aliased period of 20^d.1. The nonperiodic longer fluctuations in the X-ray intensity of Cyg X-3 are suggestive of randomly occurring ≡100^d outbursts (shot noise).