天鹅座X-1 X射线和射电发射的超轨道变化。I.旋进源的发射各向异性
Superorbital variability of X-ray and radio emission of Cyg X-1. I. Emission anisotropy of precessing sources
摘要：
我们研究的理论解释的150-d（超轨道）调制观察到的X射线和无线电发射的天鹅座X-1的模型框架连接这种现象的岁差。岁差改变发射源（圆盘或喷流）相对于观察者的方向。这导致由于源的各向异性发射图案或沿视线的吸收介质的依赖于取向的量或两者而引起的发射调制。我们认为，特别是，各向异性模式的黑体型发射，热康普顿在平板几何形状，射流/流出光束，并在光盘上方的冠状型介质中的吸收。然后，我们将这些模型与RXTE/ASM，CGRO/BATSE以及Ryle和Green Bank射电望远镜的数据进行了拟合，并找到了岁差和轨道平面之间相对较小的最佳拟合角度，约为10 - 20度。X射线发射的热康普顿化模型很好地解释了观察到的变化幅度从1到300 keV的减少，作为由于多个散射的发射的各向异性减少的结果。我们的模拟还得到喷流的整体速度为~（0.3 - 0.5）c，这与以前的限制一致，即缺乏观测到的反喷流和缺乏短期的X射线/射电相关。
英文摘要：
We study theoretical interpretations of the 150-d (superorbital) modulation observed in X-ray and radio emission of Cyg X-1 in the framework of models connecting this phenomenon to precession. Precession changes the orientation of the emission source (either disc or jet) relative to the observer. This leads to emission modulation due to an anisotropic emission pattern of the source or orientation-dependent amount of absorbing medium along the line of sight or both. We consider, in particular, anisotropy patterns of blackbody-type emission, thermal Comptonization in slab geometry, jet/outflow beaming, and absorption in a coronal-type medium above the disc. We then fit these models to the data from the RXTE/ASM, CGRO/BATSE, and the Ryle and Green Bank radio telescopes, and find relatively small best-fit angles between the precession and orbital planes, ~10-20 degrees. The thermal Comptonization model for the X-ray emission explains well the observed decrease of the variability amplitude from 1 to 300 keV as a result of a reduced anisotropy of the emission due to multiple scatterings. Our modeling also yield the jet bulk velocity of ~(0.3-0.5)c, which is in agreement with the previous constraint from the lack of an observed counterjet and lack of short-term X-ray/radio correlations.
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