MAXI J1820 +070硬态的光谱分层热吸积流
A spectrally stratified hot accretion flow in the hard state of MAXI J1820+070
摘要：
利用\nicer数据研究了黑洞X射线双星MAXI~J1820+070硬态吸积流的结构。功率谱显示宽带可变性，可以与四个洛伦兹分量在不同的时间尺度上达到峰值。提取作为能量的函数的功率谱使得能够重构这些不同功率谱分量的能谱。我们发现显着的光谱差异之间的洛伦兹，与一个对应的最短的变化时间尺度显示最难的频谱。的变异性光谱和时间平均光谱是很好的模拟由一个磁盘黑体和热康普顿，但（至少）两个不同的温度和光学深度的康普顿化区的存在是必需的。盘黑体分量是高度可变的，但仅在最长时间尺度（$\gsim1$ s）处达到峰值的可变性分量中。光谱较硬区域的种子光子主要来自较软的康普顿化区域。我们的研究结果需要在这个源的吸积流的结构，不能描述由一个单一的康普顿化区域向上散射光盘黑体光子，并从光盘的反射。
英文摘要：
We study the structure of the accretion flow in the hard state of the black-hole X-ray binary MAXI~J1820+070 with \nicer data. The power spectra show broadband variability which can be fit with four Lorentzian components peaking at different time scales. Extracting power spectra as a function of energy enables the energy spectra of these different power spectral components to be reconstructed. We found significant spectral differences among Lorentzians, with the one corresponding to the shortest variability time scales displaying the hardest spectrum. Both the variability spectra and the time-averaged spectrum are well-modelled by a disc blackbody and thermal Comptonization, but the presence of (at least) two Comptonization zones with different temperatures and optical depths is required. The disc blackbody component is highly variable, but only in the variability components peaking at the longest time scales ($\gsim1$ s). The seed photons for the spectrally harder zone come predominantly from the softer Comptonization zone. Our results require the accretion flow in this source to be structured, and cannot be described by a single Comptonization region upscattering disc blackbody photons, and reflection from the disc.
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