Coronal origin of the polarization of the high-energy emission of Cygnus X-1

Abstract

Cygnus X-1 is the candidate with the highest probability of containing a black hole among the X-ray binary systems in the Galaxy. It is also by far the most often studied of these objects. Recently, the International Gamma-Ray Astrophysics Laboratory Imager onboard then Integral satellite ({\it INTEGRAL}/IBIS) detected strong polarization in the high-energy radiation of this source, between 400 keV and 2 MeV. This radiation has been attributed to a jet launched by the black hole. We consider whether the corona around the black hole might be the site of production of the polarized emission instead of the jet. We studied self-consistently the injection of nonthermal particles in the hot, magnetized plasma around the black hole. We show that both the high-energy spectrum and polarization of Cygnus X-1 in the low-hard state can originate in the corona, without needing to invoke a jet. We estimate the degree of polarization in the intermediate state, where there is no jet, to provide a tool to test our model. Contrary to the commonly accepted view, the jet might not be the source of the MeV polarized tail in the spectrum of Cygnus X-1.

4 pages, 2 figures, accepted in A&A Letters

References in corpus (2)

• The synchrotron boiler and the spectral states of black hole binaries
• Simulating radiation and kinetic processes in relativistic plasmas

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• Lepto-hadronic model for the broadband emission of Cygnus X-1
• The INTEGRAL view on Black Hole X-ray Binaries
• Potential origin of the state-dependent high-energy tail in the black hole microquasar Cygnus X-1 as seen with INTEGRAL
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• Astroparticles from X-ray Binary Coronae
• INTEGRAL discovery of a high-energy tail in the microquasar Cygnus X-3
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• Millimeter emission from supermassive black hole coronae
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• Hard X-ray Polarimetry -- An overview of the method, science drivers and recent findings