The accretion of matter by compact objects can be inhibited by radiation pressure if the luminosity exceeds a critical value known as the Eddington limit. The discovery of ultraluminous X-ray sources has shown that accretion can proceed even when the apparent luminosity considerably exceeds this limit. A high apparent luminosity might be produced due to the geometric beaming of radiation by an outflow. The outflow half-opening angle, which determines the amplification due to beaming, has never been robustly constrained. Using the Imaging X-ray Polarimetry Explorer, we measured the X-ray polarization in the Galactic X-ray binary Cygnus X-3 (Cyg X-3). We found high, >20%, nearly energy-independent linear polarization orthogonal to the direction of the radio ejections. These properties unambiguously indicate the presence of a collimating outflow from the X-ray binary Cyg X-3 and constrain its half-opening angle to ≲15°. Thus, the source can be used as a laboratory for studying the supercritical accretion regime. This finding underscores the importance of X-ray polarimetry in advancing our understanding of accreting sources.

如果光度超过称为爱丁顿极限的临界值，则辐射压可以抑制致密物体对物质的吸积。超发光 X 射线源的发现表明，即使表观光度大大超过此极限，吸积也会继续进行。由于流出物的几何辐射束，可能会产生高表观光度。决定射束放大的流出半开角从未受到严格限制。使用成像 X 射线偏振测量探测器，我们测量了银河 X 射线双星天鹅座 X-3 (Cyg X-3) 中的 X 射线偏振。我们发现与射电喷射方向正交的高、>20%、几乎与能量无关的线性偏振。这些特性明确表明 X 射线双星 Cyg X-3 存在准直流出，并将其半张角限制为 ≲15°。因此，该源可以用作研究超临界吸积体系的实验室。这一发现强调了 X 射线偏振测量在增进我们对吸积源的理解方面的重要性。