Long term observations of Cyg X-3 with Vela 5B

Abstract

We present long-term (1969–1979) observations of Cygnus X-3, obtained by the Vela 5B satellite. The 3–12 keV light curve has 10 day time resolution. Cyg X-3 is a peculiar high-luminosity X-ray source, radiating from the radio region to hard gamma rays of more than 1016 eV. It has a 4.8 hour period, probably orbital, which is not resolved by our present analysis. Long term periodicities of ∼17, 20, and 33–34 days have been reported by several authors, and explained as the effects of apsidal motion, precession, or an eccentric orbit. We do not observe the ∼17 and 33–34 day variations, and set upper limits significantly lower than the reported amplitude of the 33–34 day variation. There is weak evidence for a 20 day flux variation. The light curve shows high and low states which alternate with a characteristic timescale of ∼1 year. There is no counterpart, at this time resolution, of the giant radio outburst of 1972 September.