Spectral variability in Cygnus X-3

We model the broad-band X-ray spectrum of Cyg X-3 in all states displayed by this source as observed by the Rossi X-ray Timing Explorer . From our models, we derive for the first time unabsorbed spectral shapes and luminosities for the full range of spectral states. We interpret the unabsorbed spectra in terms of Comptonization by a hybrid electron distribution and strong Compton reflection. We study the spectral evolution and compare with other black hole as well as neutron star sources. We show that a neutron star accretor is not consistent with the spectral evolution as a function of L _E and especially not with the transition to a hard state. Our results point to the compact object in Cyg X-3 being a massive,  ∼30 M_⊙  black hole.