  The X-ray binary Cygnus X-3 is a highly variable X-ray source that displays a
wide range of observed spectral states. One of the main states is significantly
harder than the others, peaking at ~ 20 keV, with only a weak low-energy
component. Due to the enigmatic nature of this object, hidden inside the strong
stellar wind of its Wolf-Rayet companion, it has remained unclear whether this
state represents an intrinsic hard state, with truncation of the inner disc, or
whether it is just a result of increased local absorption. We study the X-ray
light curves from RXTE/ASM and CGRO/BATSE in terms of distributions and
correlations of flux and hardness and find several signs of a bimodal behaviour
of the accretion flow that are not likely to be the result of increased
absorption in a surrounding medium. Using INTEGRAL observations, we model the
broad-band spectrum of Cyg X-3 in its apparent hard state. We find that it can
be well described by a model of a hard state with a truncated disc, despite the
low cut-off energy, if the accreted power is supplied to the electrons in the
inner flow in the form of acceleration rather than thermal heating, resulting
in a hybrid electron distribution and a spectrum with a significant
contribution from non-thermal Comptonization, usually observed only in soft
states. The high luminosity of this non-thermal hard state implies that either
the transition takes place at significantly higher L/Ledd than in the usual
advection models, or the mass of the compact object is > 20 Msun, possibly
making it the most massive black hole observed in an X-ray binary in our Galaxy
so far. We find that an absorption model as well as a model of almost pure
Compton reflection also fit the data well, but both have difficulties
explaining other results, in particular the radio/X-ray correlation.

Astrophysics