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THE SOFT GAMMA-RAY SPECTRAL VARIABILITY OF CYGNUS X-1

机译：天鹅座X-1的软伽玛射线光谱变异性

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摘要

We have used observations of Cyg X-1 from the Compton Gamma Ray Observatory and BeppoSAX to study the variation in the MeV γ-ray emission between the hard and soft spectral states, using spectra that cover the energy range from 20 keV up to 10 MeV. These data provide evidence for significant spectral variability at energies above 1 MeV. In particular, whereas the hard X-ray flux decreases during the soft state, the flux at energies above 1 MeV increases, resulting in a significantly harder γ-ray spectrum at energies above 1 MeV. This behavior is consistent with the general picture of galactic black hole candidates having two distinct spectral forms at soft γ-ray energies. These data extend this picture, for the first time, to energies above 1 MeV. We have used two different hybrid thermalonthermal Comptonization models to fit broadband spectral data obtained in both the hard and soft spectral states. These fits provide a quantitati.ve estimate of the electron distribution and allow us to probe the physical changes that take place during transitions between the low and high X-ray states. We find that there is a significant increase (by a factor of ～4) in the bolometric luminosity as the source moves from the hard state to the soft state. Furthermore, the presence of a nonthermal tail in the Comptonizing electron distribution provides significant constraints on the magnetic field in the source region.
机译：我们使用了康普顿伽玛射线天文台和BeppoSAX对Cyg X-1的观测来研究硬光谱和软光谱状态之间MeVγ射线发射的变化，使用的光谱涵盖了从20 keV到10 MeV的能量范围。这些数据为高于1 MeV的能量提供了明显的光谱可变性的证据。特别地，尽管硬X射线通量在软状态期间减小，但是在高于1 MeV的能量下通量增加，导致在高于1 MeV的能量下明显更硬的γ射线光谱。此行为与在软γ射线能量下具有两种不同光谱形式的银河黑洞候选者的总体图片一致。这些数据首次将这张图片扩展到1 MeV以上的能量。我们使用了两种不同的热/非热混合质子化模型来拟合在硬光谱和软光谱状态下获得的宽带光谱数据。这些拟合提供了电子分布的定量估计，并允许我们探究在低X射线态和高X射线态之间转换期间发生的物理变化。我们发现，随着光源从硬状态向软状态移动，辐射热亮度显着增加（约4倍）。此外，在康普顿电子分布中存在非热尾，对源区中的磁场提供了显着的约束。

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