Five Years in the Life of Cygnus X-1: BATSE Long-Term Monitoring
W. Paciesas, C. R. Robinson, M. L. McCollough, S. N. Zhang, B. A. Harmon, C. A. Wilson
Abstract
The hard X-ray emission from Cygnus X-1 has been monitored continually by BATSE since the launch of CGRO in April 1991. We present the hard X-ray intensity and spectral history of the source covering a period of more than five years. Power spectral analysis shows a significant peak at the binary orbital period. The 20-100 keV orbital light curve is roughly sinusoidal with a minimum near superior conjunction of the X-ray source and an rms modulation fraction of approximately 1.7%. No longer-term periodicities are evident in the power spectrum. We compare our results with other observations and discuss the implications for models of the source geometry.
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