Copernicus Observations of Variations in the X-Ray Flux from Cygnus X-1

Accretion Flows in Binary X-Ray Systems

“…By observing UV absorption lines and soft X-ray absorption edges we may measure column densities of highly ionized trace elements near an X-ray source, and with X-ray emission lines we may observe emission measures and velocities of the accretion flow structures. It already appears that we have seen the variable soft X-ray absorption in the spectrum of Cyg X-l (Sanford et al 1974;Holt et al 1976) predicted by Buff and McCray (1974b). Hatchett and McCray (1977) have developed methods for calculating the radiative transfer of X-rays through stellar winds in binary systems that may be used to interpret observations of Cen X-3 (Schreier et al 1976) and other such systems.…”

Celestial binary X-ray sources

“…This suggests that Cyg X-1 can be identified with the optical object HDE226862 described below. However, Sanford et al (1974) observed the above behaviour for only one binary cycle and further observations are necessary for confirmation.…”

“…At times however they find no such break and the spectral index is the range given by (5). Sanford et al (1974) using the Copernicus satellite find a = 1.6+0.1 in the 2.5-7.5 KeV range (see Section III.3.1.B.iii also). Soft X-ray measurements of Cyg X-1 have been made by Gursky et al (1971) andStevens et al (1972).…”

“…Tannanbaum et al (1972b) looked for such a periodicity in the X-ray observations of UHURU and found no evidence for such a behaviour. Sanford et al (1974) using the Copernicus satellite looked for a periodic behaviour in X-ray emission of Cyg X-1 in the 2.5-7.5 KeV range. They find a peak in the light curve at a phase 0.49+0.01, obtained using the optical binary period of 5.600 96 days, which corresponds within errors to the inferior conjunction of the secondary.…”