Correlations between X-Ray Spectral and Timing Characteristics in Cygnus X-2
Correlations between X-Ray Spectral and Timing Characteristics in Cygnus X-2
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DOI：
10.1086/520759
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发表时间：
2007-06
期刊：
影响因子：
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通讯作者：
L. Titarchuk;S. Kuznetsov;N. Shaposhnikov
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文献类型：
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作者：
L. Titarchuk;S. Kuznetsov;N. Shaposhnikov
对于一些黑洞候选源和4个中子星星（NS）源，4U 0614+09，4U 1608-52，4U 1728-34和Sco X-1，已经报道了准周期振荡（QPO）和谱幂律指数之间的相关性。本文报道了天鹅座X-2的QPO频率与指数关系的研究结果。Cyg X-2的RXTE光谱可以用一个简单的康普顿上散射的双组分模型来表示，其软光子电子温度约为0.7 keV，铁K线。推断的频谱幂律指数与低QPO频率相关。我们发现，在球面几何的框架下，康普顿云（CC）的汤姆逊光学厚度τ在~4-6之间，这与中子星星（NS）表面被遮蔽是一致的。NS的高频脉动可能是由于光子散射CC电子的结果，因为如此高的τ值被抑制。我们还指出了一些相似之处的时间（存在的低和高频率QPO）和光谱（高CC光学深度和低CC等离子体温度）之间的Cyg X-2和Sco X-1外观。
Correlations between the quasi-periodic oscillations (QPOs) and the spectral power-law index have been reported for a number of black hole candidate sources and for four neutron star (NS) sources, 4U 0614+09, 4U 1608-52, 4U 1728-34, and Sco X-1. An examination of QPO frequencies and index relationship in Cyg X-2 is reported herein. The RXTE spectrum of Cyg X-2 can be adequately represented by a simple two-component model of Compton upscattering with a soft photon electron temperature of about 0.7 keV and an iron K line. Inferred spectral power-law index shows correlation with the low QPO frequencies. We find that the Thomson optical depth of the Compton cloud (CC) τ, in framework of spherical geometry, is in the range of ~4-6, which is consistent with the surface of the neutron star (NS) being obscured. The NS high-frequency pulsations are presumably suppressed as a result of photon scattering off CC electrons because of such high values of τ. We also point out a number of similarities in terms of timing (presence of low- and high-frequency QPOs) and spectral (high CC optical depth and low CC plasma temperature) appearances between Cyg X-2 and Sco X-1.