Evaluating Spectral Models and the X-Ray States of Neutron Star X-Ray Transients
Evaluating Spectral Models and the X-Ray States of Neutron Star X-Ray Transients
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DOI：
10.1086/521181
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发表时间：
2007-02
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影响因子：
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通讯作者：
D. Lin;R. Remillard;J. Homan
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文献类型：
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作者：
D. Lin;R. Remillard;J. Homan
我们分析了中子星星（NS）的X射线瞬态Aql X-1和4U 1608-52，在20多个爆发期间获得的RXTE的X射线谱。我们测试常用的光谱模型，并评估其性能的可取性标准，包括LX的T4演化的圆盘（MCD）组件和黑洞（BH）的相似性相关的时间/光谱行为。热辐射加康普顿化的经典模型在软态下都没有很好的表现。相反，我们设计了一个混合模型：对于硬态，一个单温黑体（BB）加上一个破幂律（BPL），对于软态，两个热组件（MCD和BB）加上一个受约束的BPL。这个模型产生LX的MIT 4轨道的MCD和BB，它对齐的光谱/时间相关性，这些NS吸积BH的属性。可见的BB发射区域非常小（约为NS表面的1/16），但它在跨越硬态和软态的宽LX范围内保持大致恒定。我们讨论了一个小的和恒定的边界层的影响，在存在的最里面的稳定的圆形轨道，位于NS之外。最后，如果BB光度跟踪整体吸积率，那么我们发现，在硬态的康普顿化具有令人惊讶的高辐射效率相比，MCD在软态的排放。或者，如果我们假设，在硬状态下的喷流的辐射效率必须小于在软状态下的MCD效率，而放松有关吸积率的假设，那么我们的结果可能会建议大量的质量外流的喷流。
We analyze the X-ray spectra of the neutron star (NS) X-ray transients Aql X-1 and 4U 1608-52, obtained with RXTE during more than 20 outbursts. We test commonly used spectral models and evaluate their performance against desirability criteria, including LX ∝ T4 evolution for the multicolor disk (MCD) component and similarity to black holes (BHs) for correlated timing/spectral behavior. None of the classical models for thermal emission plus Comptonization perform well in the soft state. Instead, we devise a hybrid model: for the hard state, a single-temperature blackbody (BB) plus a broken power law (BPL), and for the soft state, two thermal components (MCD and BB) plus a constrained BPL. This model produces LX ∝ T4 tracks for both the MCD and BB, and it aligns the spectral/timing correlations of these NSs with the properties of accreting BHs. The visible BB emission area is very small (~1/16 of the NS surface), but it remains roughly constant over a wide range of LX that spans both the hard and soft states. We discuss implications of a small and constant boundary layer in terms of the presence of an innermost stable circular orbit that lies outside the NS. Finally, if the BB luminosity tracks the overall accretion rate, then we find that the Comptonization in the hard state has surprisingly high radiative efficiency compared to MCD emission in the soft state. Alternatively, if we assume that the radiative efficiency of a jet in the hard state must be less than the MCD efficiency in the soft state, while relaxing presumptions about the accretion rate, then our results may suggest substantial mass outflow in the jet.