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arXiv 0905.1086astro-ph.HE
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用康普顿散射解释Cyg X-3的特殊X射线性质

Compton scattering as the explanation of the peculiar X-ray properties of Cyg X-3

A. A. Zdziarski, R. Misra, M. Gierlinski

摘要:

我们考虑的影响可能存在的一个汤姆逊厚,低温,等离子体云周围的紧凑的对象在二进制系统天鹅座X-3。这种云的存在是早期推断的能量无关的轨道调制的X射线通量和缺乏高频率的功率谱。在这里,我们研究了云的康普顿散射对X射线能量和功率谱的影响,集中在硬谱状态。该过程降低了能谱中的高能断裂/截止的能量,这使我们能够确定汤姆逊光学深度。这一点,再加上观测到的功率谱截止值,确定了等离子体的大小为2 × 10^9 cm。在这个尺寸下,云将在X射线源的光子场中处于热平衡,这产生3 keV的云温度,这将汤姆逊光学深度的确定细化到7。在这些参数下,云的热韧致辐射也变得很重要。云的物理起源可能是沃尔夫-拉叶星伴星的非常强的恒星风与风吸积形成的小吸积盘的碰撞。我们的模型解释了天鹅座X-3独特的X射线能量和功率谱。

英文摘要:

We consider implications of a possible presence of a Thomson-thick, low-temperature, plasma cloud surrounding the compact object in the binary system Cyg X-3. The presence of such a cloud was earlier inferred from the energy-independent orbital modulation of the X-ray flux and the lack of high frequencies in its power spectra. Here, we study the effect of Compton scattering by the cloud on the X-ray energy and power spectra, concentrating on the hard spectral state. The process reduces the energy of the high-energy break/cut-off in the energy spectra, which allows us to determine the Thomson optical depth. This, together with the observed cut-off in the power spectrum, determines the size of the plasma to be 2x10^9 cm. At this size, the cloud will be in thermal equilibrium in the photon field of the X-ray source, which yields the cloud temperature of 3 keV, which refines the determination of the Thomson optical depth to 7. At these parameters, thermal bremsstrahlung emission of the cloud becomes important as well. The physical origin of the cloud is likely to be collision of the very strong stellar wind of the companion Wolf-Rayet star with a small accretion disc formed by the wind accretion. Our model thus explains the peculiar X-ray energy and power spectra of Cyg X-3.

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