Observations of three binary X-ray sources: CYG X-1, CYG X-2, and 4U1813+50 (AM HER)

A large-area, rocket-borne pointed proportional counter observation of Cygnus X-1 was made to study its spectrum from 0.15 to 20 keV, and to investigate the possible energy dependence of its "shot-noise" variability. If the column density for X-ray absorption to Cyg X-1, NX, is equal to the interstellar column density, NH, deduced from the observed reddening EB-V towards HD 226868, about half the flux in the band 0.6-1.5 keV is attributed to a steep low energy spectral component. Data from this flight, and from two previous rocket experiments sensitive in the band 1.5 to 42 keV, showed no energy dependence in their "shot-noise" behavior. The ratio of the soft component of the spectrum to the flux from the power law region of the spectrum above 2 keV is constant through the shot noise variations. Autocorrelations of data from the three flights are consistent with an energy independent shot decay time. The fraction of time-averaged flux in the shots is less than 1, confirming the result of Sutherland, Weisskopf, and Kahn (1977). The lack of rounding of the auto-correlation at very small time delays indicates that the shots must have at least one sharp edge with characteristic time ≤ 0.01 second. Cross-correlation between flux in low and high energy bands suggests a time lag, in the sense that flux at high energies lags behind that at low energies, but is consistent with zero lag. Time-skewness calculations rule out a model of exponentially decaying shots. No millisecond bursts were seen in the 84 second observation.