Why soft X-ray transients can remain in the low/hard state during outburst
Why soft X-ray transients can remain in the low/hard state during outburst
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DOI：
10.1051/0004-6361:20040369
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发表时间：
2004-08
影响因子：
--
通讯作者：
E. Meyer-Hofmeister
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文献类型：
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作者：
E. Meyer-Hofmeister
在对瞬变X射线源的典型理解中，静止时的吸积是通过外部的几何薄盘和内部以平流为主的热冕流/ADAF发生的。对辐射很重要的内部部分会产生硬光谱。在大多数震源中，爆发时光度的增加导致向软光谱的转变，这可以理解为一个多色黑体圆盘向内到达边缘稳定的轨道。一些瞬变源没有显示到软状态的这种转变。我们指出，这可以理解为在短轨道周期的系统中爆发时的峰值亮度相对较低，因此在当时较小的吸积盘中积累的质量较少。这与观测结果是一致的，观测结果表明，短轨道周期系统最有可能保持在硬光谱状态。
In the canonical understanding of transient X-ray sources the accretion during quiescence occurs via a geometrically thin disk in the outer part and via an advection-dominated hot coronal flow/ADAF in the inner part. The inner part important for the radiation yields a hard spectrum. In most sources the luminosity increase during outburst causes a change over to a soft spectrum which can be understood as that of a multi-color black body disk reaching inward to the marginally stable orbit. A few transient sources do not display this transition to the soft state. We show that this can be understood as due to relatively low peak luminosities in outburst in systems with short orbital periods and therefore less mass accumulated in the then smaller accretion disk. This is in agreement with the observations which show that most likely short orbital period systems remain in the hard spectral state.