Cyg X-1频谱的细微结构

利用线性状态空间模型（Ｌｉｎｅａｒ Ｓｔａｔｅ Ｓｐａｃｅ Ｍｏｄｅｌ－ＬＳＳＭ），将 Ｃｙｇ Ｘ－１的功率谱分解为ＬＳＳＭ产生的模型功率谱和剩余功率谱两部分．集中分析剩余功率谱，结果显示， Ｃｙｇ Ｘ－１在低／硬态、转换态和高／软态三种状态的剩余功率谱有着不同的结构特征．其中高／软态和低／硬态的剩余功率谱存在一个宽峰结构，中心频率分别为～ ８ Ｈｚ和～ ５ Ｈｚ，低／硬态的剩余功率诺在～ ０．０７ Ｈｚ达到极大；转换态的剩余功率谱有双峰结构，其中心频率分别在～０．５—４Ｈｚ和～５—１１Ｈｚ，与我们以前分析的 ＱＰＯ的中心频率很接近，说明 ＱＰＯ与线性状态空间所要求的自回归模型可能属于不同的物理过程．与总功率谱比较，剩余功率谱对谱的变化部分（例如ＱＰＯ、截断频率等）更为敏感，本文对剩余功率谱中谱峰变化的原因做了初步的探讨．

The Fine Spectral Structure of Cygnus X-1

The power spectral density (PSD) of Cyg X-1 is divided into two parts by using the linear state space model (LSSM). One part is the PSD of LSSM, the other is the residual power spectral density (RPSD) defined by the whole PSD minus the model PSD. We focus our attention on analyzing the RPSD. The results show that RPSD has different characteristics in 3 different states-the low/hard, transition and high/soft states. There is a broad peak structure both in the high/soft and low/hard states, with average central frequencies ~ 8Hz and ~ 5 Hz respectively. The RPSD in the low/hard state may peak at ~ 0.07Hz. While during the transition State, the RPSD has a double-peak structure, with the central frequencies in the regions of 0.5-4Hz and 5-11 Hz respectively, and these are quite close to the QPO central frequencies we have previously obtained. This fact implies that the QPO and the auto-regression that is needed in LSSM belong to different physical processes. Comparing to PSD, the RPSD is more sensitive to variations, such as the QPO, the broken frequencies and so on, The reason for the variable peak in the RPSD is discussed.