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Short-term variability of Cyg X-1 and the accretion disk temperature fluctuation

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Abstract

Recent thoretical models of Cyg X-1 (refs 1–5) assume that to explain the observed time-averaged spectrum the hard X rays are emitted by inverse-Compton mechanism from an optically thin, hot accretion disk around a black hole. Numerous observations (especially in the energy range20 ke V) have shown that the source intensity is variable on different time scales6–17. Short-term variability on the time scale of 1 s is especially conspicuous because of its stationary nature and the stability of time scale6–11. A balloon observation was carried out to study the variability in the hitherto unknown hard X-ray range (20 ke V). The results of the analysis, together with those of the former rocket observation, suggest that the variation is essentially spectral, implicating that it originates from temperature fluctuation in an accretion disk. Such a model is discussed here in detail.

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