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Aims: The nature of Cygnus X-3 is still not understood well. This binarysystem might host a black hole or a neutron star. Recent observations byINTEGRAL have shown that Cygnus X-3 was again in an extremely ultrasoft state.Here we present our analysis of the transition from the ultrasoft state,dominated by blackbody radiation at soft X-rays plus non-thermal emission inthe hard X-rays, to the low hard state.  Methods: INTEGRAL observed Cyg X-3 six times during three weeks in late Mayand early June 2007. Data from IBIS/ISGRI and JEM-X1 were analysed to show thespectral transition.  Results: During the ultrasoft state, the soft X-ray spectrum iswell-described by an absorbed (NH = 1.5E22 1/cm**2) black body model, whereasthe X-ray spectrum above 20 keV appears to be extremely low and hard (Gamma =1.7). During the transition, the radio flux rises to a level of >1 Jy, and thesoft X-ray emission drops by a factor of 3, while the hard X-ray emission risesby a factor of 14 and becomes steeper (up to Gamma = 4).  Conclusions: The ultrasoft state apparently precedes the emission of a jet,which is apparent in the radio and hard X-ray domain.

Cygnus X-3 transition from the ultrasoft to the hard state