Hard X-ray observations of cygnus X-3

Abstract

Hard X-ray observations of Cyg X-3, obtained with the large area proportional counter telescope flown on a balloon on 18 March 1986, are presented. The source was observed for a duration about 2 h spanning the 4.8 h binary cycle. The integral intensity of the source in the 20-100 keV range shows a strong 4.8 h modulation with a broad maximum between the binary phases 0.3 and 0.7. The observed spectrum flux during the maximum intensity is well fitted with a power law spectrum of index of 2.8 ± 0.5. Fourier analysis of the data during the maximum intensity shows a periodicity at 121 s, which is attributed to transient oscillations of the type seen at the lower energies.