AI 中文总结
本研究通过VLBI观测Swift J1727.8-1613的爆发，追踪喷流knot运动，发现其喷流速度、洛伦兹因子等特性不由黑洞质量等固定参数唯一决定。
AI 中文摘要
我们展示了2023-2024年黑洞低质量X射线双星（LMXB）Swift J1727.8-1613爆发期间，甚长基线干涉测量（VLBI）密集观测 campaign 的结果。我们观测到在硬中间态与软中间态的多次跃迁过程中，高度延展的连续喷流反复熄灭与重建，以及瞬态喷流的多次抛射。通过时变可见度模型拟合，我们追踪了9个离散喷流 knot 的运动，获得了LMXB中瞬态喷流自行和抛射日期的最精确测量结果之一。这些抛射物仅在VLBI观测中可被短时间探测，部分呈现出观测时段内快速的流量密度变化，而这一变化未在图像重建中被捕捉。我们首次采用时变可见度建模对喷流 knot 的流量密度进行分段模型拟合，得以构建其观测时段内变异性的复杂非参数光变曲线。我们在多次态跃迁中观测到多个抛射物的发射，但在可用的X射线强度或硬度数据中未识别到喷流抛射的一致特征。我们约束了喷流 knot 的本征速度和整体洛伦兹因子，发现Swift J1727.8-1613在整个爆发期间既发射了弱相对论性也发射了高度相对论性的抛射物。我们利用其自行约束了喷流轴最大倾角的后验分布，其中第50、84、99百分位数分别为40°、50°、66°。单个LMXB多次抛射瞬态喷流的这些独特观测表明，黑洞质量、黑洞自旋、自旋-轨道错位等固定参数并不能唯一确定瞬态喷流的变化特性，尤其是其速度和洛伦兹因子。
英文摘要
We present the results of our intensive VLBI campaign on the black-hole low-mass X-ray binary (LMXB) Swift J1727.8-1613 during its 2023-2024 outburst. We observed the repeated quenching and re establishment of the highly-extended continuous jet during several transitions between hard-intermediate and soft-intermediate states, and the repeated ejection of transient jets. Using time-dependent visibility model fitting, we tracked the motion of nine discrete jet knots, obtaining some of the most precise measurements of transient jet proper motions and ejection dates in an LMXB. These ejecta were only detectable for a short time with VLBI, and some showed rapid intra-observation flux density variability that was not captured in image reconstructions. For the first time, we use time-dependent visibility modelling to fit a piecewise model for the jet knot flux densities, allowing us to create complex, non-parametric light curves of their intra-observation variability. We observed the launching of multiple ejecta across several state transitions, however, we could not identify a consistent signature of jet ejection in the available X-ray intensity or hardness data. We constrained the intrinsic speeds and bulk Lorentz factors of the jet knots, finding that Swift J1727.8-1613 launched both mildly relativistic and highly relativistic ejecta throughout its outburst. We used their proper motions to constrain a posterior distribution for the maximum inclination angle of the jet axis, which had 50th, 84th, and 99th percentiles of 40°, 50°, and 66°, respectively. These unique observations of the repeated ejection of transient jets by a single LMXB reveal that fixed parameters such as black-hole mass, black-hole spin, and spin-orbit misalignment do not uniquely determine the varying properties of transient jets, particularly their speeds and Lorentz factors.
Comments26 pages, 19 figures, 5 tables. Accepted for publication by PASA
