The existence of relatively cool (kBT ≲ 10 keV) and optically thick (τ ≳ 3) coronae are inferred above super-Eddington accretion flow such as ultraluminous X-ray sources, GRS 1915+105, and narrow-line Seyfert 1 galaxies, which contrasts with cases in sub-Eddington accretion flows, which are associated with coronae with kBT ∼ 100 keV and τ ∼ 1. To understand their physical origin, we investigate the emission properties of the corona which is formed by the gas blown off the super-Eddington inner disk by radiation pressure. We assume that the corona is heated by the reconnection of magnetic loops emerging from the underlying disk. We show that this radiation-pressure-driven wind can act as an optically thick corona which upscatters thermal soft photons from the underlying disk, and that with a reasonable parameter set we can theoretically reproduce the coronal optical depth and temperature which are inferred by spectral fittings of observational data. By contrast, the coronal optical depth cannot be so high in sub-Eddington cases, since the coronal material is supplied from the disk via evaporation and there is a maximum limit on the evaporation rate. We suggest that low-temperature, optically thick Comptonization should be a key signature of super-Eddington accretion flow.

中文翻译：

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是什么决定了超级爱丁顿吸积体的独特光谱？超爱丁顿吸积流中光学厚和低温日冕的起源

在超爱丁顿吸积流之上推断出存在相对较冷（kBT ≲ 10 keV）和光学厚（τ ≳ 3）的日冕，例如超亮 X 射线源、GRS 1915+105 和窄线 Seyfert 1 星系，它们与亚爱丁顿吸积流中的情况形成对比，后者与 kBT ∼ 100 keV 和 τ ∼ 1 的日冕有关。为了了解它们的物理起源，我们研究了由超-吹出的气体形成的日冕的发射特性爱丁顿内盘受辐射压。我们假设日冕是通过从下面的磁盘中出现的磁环的重新连接而加热的。我们表明，这种由辐射压力驱动的风可以充当光学厚日冕，向上散射来自下方圆盘的热软光子，并且通过合理的参数设置，我们理论上可以再现由观测数据的光谱拟合推断出的日冕光学深度和温度。相比之下，在亚爱丁顿情况下，冠状光学深度不能这么高，因为冠状材料是通过蒸发从圆盘提供的，并且蒸发速率存在最大限制。我们建议低温、光学厚的康普顿化应该是超爱丁顿吸积流的一个关键特征。