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The bright and highly variable X-ray and radio source known as Cygnus X-3 wasamong the first X-ray sources discovered, yet it remains in many ways anenigma. Its known to consist of a massive, Wolf-Rayet primary in an extremelytight orbit with a compact object. Yet one of the most basic of parameters -the mass of the compact object - is not known. Nor is it even clear whether itsis a neutron star or a black hole. In this Paper we present our analysis of thebroad-band high-energy continua covering a substantial range in luminosity andspectral morphology. We apply these results to a recently identified scalingrelationship which has been demonstrated to provide reliable estimates of thecompact object mass in a number of accretion powered binaries. This analysisleads us to conclude that the compact object in Cygnus X-3 has a mass greaterthan $4.2M_\odot$ thus clearly indicative of a black hole and as such resolvinga long-standing issue. The full range of uncertainty in our analysis and fromusing a range of recently published distance estimates constrains the compactobject mass to lie between $4.2M_\odot$ and $14.4M_\odot$. Our favoredestimate, based on a 9.0 kpc distance estimate is $\sim 10 M_\odot$ with theerror margin of 3.2 solar masses. This result may thus pose challenges toshared-envelope evolutionary models of compact binaries, as well asestablishing Cygnus X-3 as the first confirmed accretion-powered galacticgamma-ray source.

New Evidence for a Black Hole in the Compact Binary Cygnus X-3