Spectral variability of Cyg X-1 using INTEGRAL data

Alexandros Filothodoros, Piotr Lubiński and Andrzej A. Zdziarski

The studies of the spectral states are an important diagnostic tool of the black hole binary systems and Cyg X-1 is one of the most well analyzed objects in this aspect. We present a novel approach, using the 13-years INTEGRAL data of Cyg X-1 for the spectral identification based on the hard X-ray emission, which results in a more unambiguous selection between the hard and soft spectral states. Based on this classification, the INTEGRAL/ISGRI data were split into 12 groups (substates) with a similar total exposure time. The ISGRI spectra of each substate were analyzed together with contemporary INTEGRAL/JEMX spectra using two advanced Comptonization models. The spectral analysis allowed us to find a correspondence between the physical model parameters of the system and the phenomenological classification based on the ISGRI count rates. In particular, we investigated the evolution of the thermal and non-thermal plasma properties on the hard X-ray hardness ratio.

Proceedings of the Polish Astronomical Society, vol. 7, 326-329 (2018)

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