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Y. Yao, S. N. Zhang, X. L. Zhang, Y. X. Feng (UAH/NSSTC)
As the first dynamically determined black hole X-ray binary system, Cygnus X-1 has been studied extensively. However, its broad-band spectra in hard state with BeppoSAX is still not well understood. Besides the soft excess described by the multi-color disk model (MCD), the power-law component and a broad excess feature above 10 keV (disk reflection component), there is also an additional soft component around 1 keV, whose origin is not known currently. Here we propose that the additional soft component is due to the thermal Comptonization process between the soft disk photon and the warm plasma cloud just above the disk, i.e., a warm layer. We use Monte-Carlo technique to simulate this Compton scattering process and build several table models based on our simulation results. With these table models, we study the disk structure in Cygnus X-1. According to the fitting results with our table models, the electron energy distribution in the corona follows the Maxwellian form and if the warm layer we proposed here is the commonly observed outflow in x-ray binary system, the outflow velocity is about 0.01-0.02 c in Cygnus X-1.
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.