Report

Polarized Gamma-Ray Emission from the Galactic Black Hole Cygnus X-1

Science  22 Apr 2011:
Vol. 332, Issue 6028, pp. 438-439
DOI: 10.1126/science.1200848

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  1. Fig. 1

    Cygnus X-1 energy spectrum as measured by the INTEGRAL/IBIS telescope and obtained with the standard IBIS spectral analysis pipeline. Two components are clearly seen: a “Comptonization” spectrum caused by photons upscattered by Compton scattering off thermally distributed electrons in a hot plasma (dashed line), and a higher-energy component (solid line) whose origin is not known.

  2. Fig. 2

    Cygnus X-1 polarization signal measured in two adjacent energy bands. This distribution gives the source count rate by azimuthal angle of the Compton scattering. In the 250- to 400-keV energy band (A), the signal is consistent with a flat signal, indicating that the observed gamma rays are weakly polarized, or even not polarized. In the 400- to 2000-keV energy band (B), the signal is now highly modulated, indicating that the observed gamma rays are highly polarized.