黑洞X射线双星Swift J1727.8-1613中稳定的X射线回响滞后
Stable X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613
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中文总结 AI 辅助
研究黑洞X射线双星Swift J1727.8-1613在2023年爆发期间X射线回响滞后演变，通过分析NICER观测数据，计算时间滞后并构建相关谱，发现HIMS期间回响滞后变化小，为研究吸积几何结构演变提供新见解。
中文摘要 AI 辅助
目的：研究黑洞X射线双星Swift J1727.8-1613在2023年爆发期间X射线回响滞后的演变，以探究跨光谱状态的内吸积流几何结构。方法：分析了覆盖低硬态（LHS）和硬中间态（HIMS）的NICER观测数据。使用基于傅里叶的技术计算时间滞后，并构建滞后频率和滞后能量谱。为获得软滞后幅度的稳健估计，聚焦于回响信号占主导且稳定的频率范围，以最小化硬滞后和相位缠绕效应的污染。结果：软滞后幅度从LHS到早期HIMS迅速增加，然后在整个HIMS期间保持在10毫秒左右。在回响滞后占主导的频率范围内，滞后对傅里叶频率的依赖性很小。另一方面，观测到的低频滞后从硬滞后主导变为软滞后主导，幅度与在较高频率测量的幅度相当。结论：这些结果表明，在HIMS期间回响滞后变化不大，与该状态下相对稳定的内吸积几何结构一致。从LHS到HIMS的滞后幅度的明显演变在很大程度上可以由硬滞后效应的减弱来解释，不一定需要内在光传播时间尺度的显著变化。因此，Swift J1727.8-1613提供了一个案例，其中可以在较宽频率范围内以减少的污染研究回响信号，为黑洞X射线双星吸积几何结构的演变提供了新的见解。
英文摘要
Aims. We investigate the evolution of X-ray reverberation lags in the black hole X-ray binary Swift J1727.8-1613 during its 2023 outburst, with the aim of probing the inner accretion flow geometry across spectral states. Methods. We analyzed NICER observations covering the low-hard state (LHS) and hard-intermediate state (HIMS). The time lags were computed using Fourier-based techniques, and we constructed lag-frequency and lag-energy spectra. To obtain a robust estimate of the soft lag amplitude, we focused on a frequency range in which the reverberation signal dominates and remains stable, thereby minimizing contamination from hard lags and phase-wrapping effects. Results. The soft lag amplitude increases rapidly from the LHS to the early HIMS and then stays near 10 ms throughout the HIMS. In the frequency range in which reverberation lags prevail, the lag shows little dependence on Fourier frequency. On the other hand, the observed low-frequency lags change from hard-lag dominated to soft-lag dominated, with amplitudes comparable to those measured at higher frequencies. Conclusions. These results suggest that the reverberation lag varies little during the HIMS, consistent with a relatively stable inner accretion geometry during this state. The apparent evolution of the lag amplitude from the LHS to the HIMS can be largely explained by the diminishing effect of hard lags and does not necessarily require significant changes in the intrinsic light-travel timescale. Swift J1727.8-1613 therefore provides a case in which the reverberation signal can be studied with reduced contamination over a broad frequency range, offering new insight into the evolution of the accretion geometry in black hole X-ray binaries.
