* Astronomy

Cyg X-3's Little Friend: A Stellar Circle of Life

In 2003, astronomers presented results using Chandra's high-resolution vision in X-rays to identify a mysterious source of X-ray emission located very close to Cygnus X-3 on the sky (smaller white object to the upper left). The separation of these two sources is equivalent to the width of a penny about 800 feet away. A decade later, astronomers reported the new source is a cloud of gas and dust. In astronomical terms, this cloud is rather small - about 0.7 light years in diameter or under the distance between the Sun and Pluto's orbit.
Astronomers realized that this nearby cloud was acting as a mirror, reflecting some of the X-rays generated by Cygnus X-3 towards Earth. They nicknamed this object the "Little Friend" due to its close proximity to Cygnus X-3 on the sky and because it also demonstrated the same 4.8-hour variability in X-rays seen in the X-ray binary.
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Title: Cygnus X-3's Little Friend
Authors: Michael L. McCollough, Randall K. Smith, Lynne Valencic

Using the unique X-ray imaging capabilities of the Chandra observatory, a 2006 observation of Cygnus X-3 has provided insight into a singular feature associated with this well-known microquasar. This extended emission, located ~16 arcseconds from Cygnus X-3, varies in flux and orbital phase (shifted by 0.56 in phase) with Cygnus X-3, acting like a celestial X-ray "mirror". The feature's spectrum, flux and time variations allow us to determine the location, size, density, and mass of the scatterer. We find that the scatterer is a Bok globule located along our line of sight, and discuss its relationship to Cygnus X-3. This is the first time such a feature has been identified with the Chandra X-ray Observatory.

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Title: New Evidence for a Black Hole in the Compact Binary Cygnus X-3
Authors: Chris Shrader, Lev Titarchuk, Nikolai Shaposhnikov

The bright and highly variable X-ray and radio source known as Cygnus X-3 was among the first X-ray sources discovered, yet it remains in many ways an enigma. Its known to consist of a massive, Wolf-Rayet primary in an extremely tight 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 its is a neutron star or a black hole. In this Paper we present our analysis of the broad-band high-energy continua covering a substantial range in luminosity and spectral morphology. We apply these results to a recently identified scaling relationship which has been demonstrated to provide reliable estimates of the compact object mass in a number of accretion powered binaries. This analysis leads us to conclude that the compact object in Cygnus X-3 has a mass greater than 4.2 solar masses thus clearly indicative of a black hole and as such resolving a long-standing issue. The full range of uncertainty in our analysis and from using a range of recently published distance estimates constrains the compact object mass to lie between 4.2 solar masses and 14.4 solar masses. Our favoured estimate, based on a 9.0 kpc distance estimate is ~ 10 solar masses with the error margin of 3.2 solar masses. This result may thus pose challenges to shared-envelope evolutionary models of compact binaries, as well as establishing Cygnus X-3 as the first confirmed accretion-powered galactic gamma-ray source.

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Credit: NASA/DOE/Fermi LAT Collaboration

Brighter colours indicate greater numbers of gamma rays detected in this Fermi LAT view of a region centred on the position of Cygnus X-3 (circled). The brightest sources are pulsars.

Position(2000): RA 20 32 25.78, Dec +40 57 27.9