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RXTE Observation of Cygnus X-1 In Its High State

W. Cui·W. A. Heindl·R. E. Rothschild·S. N. Zhang·K. Jahoda·W. Focke
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Abstract

We present the results from the RXTE observations of Cygnus X-1 in its high state. In the energy range of 2-200 keV, the observed X-ray spectrum can be described by a model consisting of a soft blackbody component and a broken power-law with a high energy cutoff. The low energy spectrum (below about 11 keV) varies significantly from observation to observation while the high energy portion changes little. The X-ray flux varies on all timescales down to milliseconds. The power density spectrum (PDS) can be characterized by excess red noise (``1/f'') at low frequencies and a white noise component that extends to 1-3 Hz before being cut off. At higher frequencies, the PDS becomes power-law again, with a slope of roughly -2 (i.e., ``1/f^2''). Broad peaks in the range of 3-9 Hz are present, and might be due to quasi-periodic oscillations. The PDS shows interesting spectral dependence: the 1/f component becomes more prominent when the low-energy spectrum becomes softer. The difference in the observed spectral and timing properties between the low and high states is qualitatively consistent with a simple ``fluctuating corona'' model.

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W. Cui, W. A. Heindl, R. E. Rothschild, S. N. Zhang, K. Jahoda, W. Focke. 1996-10-10. RXTE Observation of Cygnus X-1 In Its High State. https://doi.org/10.1086/310419

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