超铝X射线源光子泡模型的X射线谱特征
X-ray Spectral Signatures of the Photon Bubble Model for Ultraluminous X-ray Sources
摘要：
邻近星系中超亮X射线源的性质是现代X射线天体物理学中的一个重要问题。对这些物体的一种可能的解释是围绕$\sim 10 M_{\odot}$黑洞的非均匀的、辐射主导的吸积盘--所谓的"光子泡“模型。虽然以前的研究主要集中在这个模型的辐射流体力学方面，在本文中，我们提供了一个分析其X射线光谱（连续和可能的边缘和线）的特点。盘中高密度区和低密度区之间的康普顿反射可能提供了区分这种模型与其他模型的关键，例如吸积到中等质量黑洞上。我们耦合的Monte Carlo/Fokker-Planck辐射输运程序与XSTAR代码的反射模拟光子气泡模型中产生的光子光谱的ULXs。我们发现，反射分量往往是非常弱的，在大多数情况下是不可观察的，并作出预测的形状的高能康普顿化谱。在许多情况下，康普顿化甚至在低至$\sim$几keV的光谱中占主导地位。在一个模拟中，发现了一个$\sim 9 \kev$功能，这可能被认为是ULX中光子气泡的签名;此外，我们预测了未来仪器可能观察到的高能幂律。
英文摘要：
The nature of ultraluminous X-ray sources in nearby galaxies is one of the major open questions in modern X-ray astrophysics. One possible explanation for these objects is an inhomogeneous, radiation dominated accretion disk around a $\sim 10 M_{\odot}$ black hole -- the so-called ``photon bubble'' model. While previous studies of this model have focused primarily on its radiation-hydrodynamics aspects, in this paper, we provide an analysis of its X-ray spectral (continuum and possible edge and line) characteristics. Compton reflection between high and low density regions in the disk may provide the key to distinguishing this model from others, such as accretion onto an intermediate mass black hole. We couple a Monte Carlo/Fokker-Planck radiation transport code with the XSTAR code for reflection to simulate the photon spectra produced in a photon bubble model for ULXs. We find that reflection components tend to be very weak and in most cases not observable, and make predictions for the shape of the high-energy Comptonizing spectra. In many cases the Comptonization dominates the spectra even down to $\sim$ a few keV. In one simulation, a $\sim 9 \kev$ feature was found, which may be considered a signature of photon bubbles in ULXs; furthermore, we make predictions of high energy power-laws which may be observed by future instruments.
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