The pulsating X-ray source Cyg X-1 has been reported as having various conflicting or changing periodicities, or as being nonperiodic. The reported data have been reanalyzed in an effort to clarify this situation, and are found to be indistingnishable from shot noise due to short overlapping outbursts of X-ray emission, with no true periodicity. Computer-generated shot-noise data have the same appearance and lead to similar power spectra. The observational data are consistent with random pulses which have an effective pulse length of 0.3 + 0.1 s and occur at varying rates of the order of several hundred per second. The pulse length indicates a maximum source size of 0.8 light-seconds. It is suggested that some other fluctuating X-ray sources, such as Sco X-1 and Cir X-1, may also have such a shot-noise character.
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Jr. Terrell N. James (1972) studied this question.