  Long observation (1972 - 2009) of the powerful discrete source in Galaxy
Cygnus X-3 discovered its main properties and let to develop a real model of
this unique object. It is short binary system with 4.8 hour orbital period
including relativistic object (neutron star or black hole) and massive star.
Source most activity is seen in gamma-rays from tens MeV to thousands TeV.

High Energy Astrophysical Phenomena;Astrophysics of Galaxies;Instrumentation and Methods for Astrophysics