Title: Evolution of the Comptonizing medium of the black-hole candidate Swift J1727.8$-$1613 along the hard to hard-intermediate state transition using NICER Show Chinese title

Title: 黑洞候选体 Swift J1727.8$-$1613 在硬态到硬-中间态转换过程中康普顿化介质的演化使用 NICER

Abstract: We analyse the properties of the Comptonizing medium in the black-hole X-ray binary Swift J1727.8$-$1613 using the time-dependent Comptonization model vkompth, using NICER observations of type-C QPOs in the hard and hard-intermediate states. During the 2023 outburst of the source, we measure the rms and phase lags of the QPO across 45 observations as the QPO frequency, $\nu_{\rm QPO}$, evolves from $\sim 0.3$ Hz to $\sim 7$ Hz. By simultaneously fitting the time-averaged spectrum of the source and the rms and lag spectra of the QPO, we derive the evolution of the disk and corona parameters. At $\nu_{\rm QPO} = 0.34$ Hz, the QPO phase lags are hard, with 10 keV photons lagging 0.5 keV photons by $\sim 0.5$ rad. As $\nu_{\rm QPO}$ increases, the lags for the same energy bands decrease, reaching near zero at $\nu_{\rm QPO} \sim 1.2$ Hz, and then reverse to soft lags of $\sim -1.1$ rad at $\nu_{\rm QPO} \sim 7$ Hz. Initially, the inner radius of the accretion disk is truncated at $\sim 30-40 R_g$ (assuming a 10 solar-mass black hole) and, as the QPO frequency increases, the truncation radius decreases down to $\sim 10 R_g$. Initially, two coronas of sizes of $\sim 6.5 \times 10^3$ km and $\sim 2 \times 10^3$ km, extend over the disk and are illuminated by different regions of the disk. As the QPO frequency increases, both the coronas shrink to $\sim 2 \times 10^3$ km at $\nu_{\rm QPO} = 2.5$ Hz. Following a data gap, one corona expands again, peaking at a size of $\sim 2 \times 10^4$ km. We interpret the evolution of the coronal size in the context of accompanying radio observations, discussing its implications for the interplay between the corona and the jet. Show Chinese abstract

Abstract: 我们分析了使用时间依赖性康普顿化模型 vkompth 对黑洞 X 射线双星 Swift J1727.8$-$1613 的康普顿化介质的特性，利用 NICER 在硬态和硬中间态中对类型 C QPO 的观测。在源的 2023 年爆发期间，我们在 45 次观测中测量了 QPO 的均方根和相位滞后，随着 QPO 频率$\nu_{\rm QPO}$从$\sim 0.3$Hz 变化到$\sim 7$Hz。通过同时拟合源的时间平均谱和 QPO 的均方根和滞后谱，我们得出了盘和冕参数的演化。在$\nu_{\rm QPO} = 0.34$Hz 时，QPO 相位滞后是硬的，10 keV 光子比 0.5 keV 光子滞后$\sim 0.5$rad。 随着$\nu_{\rm QPO}$的增加，相同能带的时滞减小，在$\nu_{\rm QPO} \sim 1.2$Hz 时接近零，然后在$\nu_{\rm QPO} \sim 7$Hz 时变为软时滞$\sim -1.1$弧度。 最初，吸积盘的内半径被截断在$\sim 30-40 R_g$（假设一个10倍太阳质量的黑洞），并且随着QPO频率的增加，截断半径减小到$\sim 10 R_g$。 最初，两个大小分别为$\sim 6.5 \times 10^3$公里和$\sim 2 \times 10^3$公里的日冕扩展到盘面上，并由盘的不同区域照亮。 随着QPO频率的增加，两个日冕缩小到$\sim 2 \times 10^3$公里，在$\nu_{\rm QPO} = 2.5$赫兹时达到。 在数据间隙之后，一个日冕再次扩展，达到$\sim 2 \times 10^4$公里的最大尺寸。 我们根据伴随的射电观测来解释日冕大小的演化，讨论其对日冕与喷流之间相互作用的意义。