Cygnus X-1 - A two-temperature accretion disk model which explains the observed hard X-ray spectrum

We present a model for Cygnus X-1, involving an accretion disk around a black hole, which fits the observed X-ray spectrum from 8 to 500 keV. The hard component of the spectrum (E>8 keV) is produced by an optically thin inner portion of the disk in which the electrons are 10$sup 9$ K and the ions are 3-- 300 times hotter.