Observations of Cyg X-1 and Cyg X-3 Above 7 keV from OSO-7

Abstract

The UCSD cosmic X-ray telescope onboard the OSO-7 satellite scanned Cygnus X-1 and X-3 in the 7 to 250 keV range during December 17–24, 1971. These observations are of interest for several reasons. First, the Cyg X-1 data below 20 keV confirm the results of Tananbaum et al.¹, who report no eclipse in the 2–20 keV range with a period between 2 and 6.2 d. Second, synchrotron emission and inverse Compton scattering models for Cyg X-1 have been proposed respectively by Dolan² and Jackson³, predicting variability at the 5.6 d binary period that should be seen only at energies above 20 keV. For Cyg X-3, the data are at slightly higher energies than those of Parsignault et al.⁴ and Canizares et al.⁵ who have reported a 4.8 h cyclic variation at X-ray energies. Our data may add information on the energy dependence of this effect. We also present spectra which, when combined with other observations, may indicate long term changes in the sources.