发表机构
School of Physics and Technology, Wuhan University; Newcastle University; Universitat Politècnica de Catalunya; Institut d’Estudis Espacials de Catalunya（武汉大学物理科学与技术学院; 纽卡斯尔大学; 加泰罗尼亚理工大学; 加泰罗尼亚空间研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过蒙特卡洛模拟揭示外流日冕的谱与时变特征，可区分日冕外流与盘截断情景，并解释MAXI J1820+070的异常相关性。
AI 中文摘要
黑洞X射线双星（BHXRBs）中的日冕在爆发期间很可能是动态的。已有研究提出，一个中等相对论性外流日冕可以解释X射线双星硬态中观测到的硬谱、弱盘反射以及高于预期的偏振度。在本工作中，我们利用蒙特卡洛辐射转移模拟研究了日冕外流的谱与时变效应。该模型由一个几何薄、光学厚的截断盘和一个具有预设体向外流速度的椭球日冕组成。我们计算了不同外流速度和盘截断半径下的康普顿化连续谱、盘反射成分以及滞后-频率谱。我们发现，增加外流速度会通过相对论性集束效应降低反射分数，因为更少的康普顿化光子照射到盘上。对于β≲0.5，高频软滞后仅受外流速度的微弱影响，而增加盘截断半径会将零交叉频率（ν0）移至显著更低的频率。因此，时变特性有助于区分日冕外流情景与盘截断情景。我们进一步将该模型应用于MAXI J1820+070，发现其在平台阶段不寻常的R-Γ反相关与日冕收缩伴随体速度增加定性一致。仅盘退缩在我们的模型假设下将预测ν0相反的演化。未来的偏振计算将为扩展外流日冕模型提供额外的检验。
英文摘要
The corona in black hole X-ray binaries (BHXRBs) is likely dynamic during outbursts. A mildly relativistic outflowing corona has been proposed to explain hard spectra, weak disk reflection, and the higher than expected polarization degree observed in the hard state of X-ray binaries. In this work, we investigate the spectral and timing effects of coronal outflow using Monte Carlo radiative-transfer simulations. The model consists of a geometrically thin, optically thick truncated disk and an ellipsoidal corona with a prescribed bulk outflow velocity. We calculate the Comptonized continuum, the disk reflection component, and the lag-frequency spectra for different outflow velocities and disk truncation radii. We find that increasing the outflow velocity reduces the reflection fraction through relativistic beaming, because fewer Comptonized photons irradiate the disk. For $β\lesssim 0.5$, the high-frequency soft lag is only weakly affected by the outflow velocity, whereas increasing the disk truncation radius shifts the zero-crossing frequency($ν_0$) to substantially lower frequencies. Thus, timing properties can help distinguish the coronal-outflow scenario from the disk-truncation scenario. We further apply the model to MAXI J1820+070 and find that its unusual $R-Γ$ anti-correlation during the plateau phase is qualitatively consistent with a contracting corona accompanied by increasing bulk velocity. Disk recession alone would predict the opposite evolution of $ν_0$ under the assumptions of our model. Future polarization calculations will provide an additional test of extended outflowing-corona models.
Comments16 pages, 10 figures
