We perform broadband (0.7–100 keV) spectral analysis of five hard state observations of the low-mass black hole X-ray binary GX 339–4 taken by AstroSat during the rising phase of three outbursts from 2019 to 2022. We find that the outburst in 2021 was the only successful/full outburst, while the source was unable to make the transition to the soft state during the other two outbursts in 2019 and 2022. Our spectral analysis employs two different model combinations, requiring two separate Comptonizing regions and their associated reflection components and soft X-ray excess emission. The harder Comptonizing component dominates the overall bolometric luminosity, while the softer one remains relatively weak. Our spectral fits indicate that the disk evolves with the source luminosity, where the inner disk radius decreases with increasing luminosity. However, the disk remains substantially truncated throughout all the observations at the source luminosity of ∼2%–8%× of the Eddington luminosity. We note that our assumption of the soft X-ray excess emission as disk blackbody may not be realistic, and this kind of soft excess may arise due the nonhomogeneity in the disk/corona geometry. Our temporal analysis deriving the power density spectra suggests that the break frequency increases with the source luminosity. Furthermore, our analysis demonstrates a consistency between the inner disk radii estimated from the break frequency of the power density spectra and those obtained from the reflection modeling, supporting the truncated disk geometry in the hard state.

中文翻译：

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GX 339–4 在硬状态下的吸积几何：AstroSat 视图


我们对 AstroSat 在 2019 年至 2022 年三次爆发的上升阶段拍摄的低质量黑洞 X 射线双星 GX 339-4 的五次硬态观测进行了宽带（0.7-100 keV）光谱分析。我们发现2021 年的爆发是唯一一次成功/完全爆发，而在 2019 年和 2022 年的另外两次爆发期间，源无法过渡到软状态。我们的光谱分析采用两种不同的模型组合，需要两个单独的 Comptonizing 区域及其相关的反射分量和软X射线过量发射。较硬的 Comptonizing 成分在整体测辐射热亮度中占主导地位，而较软的成分仍然相对较弱。我们的光谱拟合表明圆盘随着光源光度的变化而演化，其中圆盘内半径随着光度的增加而减小。然而，在源光度为爱丁顿光度的~2%–8%×的所有观测中，圆盘仍然基本上被截断。我们注意到，我们对软 X 射线过量发射作为盘黑体的假设可能不现实，并且这种软过量可能是由于盘/日冕几何形状的不均匀性而出现的。我们推导出功率密度谱的时间分析表明，拐点频率随着源光度的增加而增加。此外，我们的分析证明了根据功率密度谱的拐点频率估计的内盘半径与通过反射建模获得的内盘半径之间的一致性，支持硬状态下的截断盘几何形状。