标题： 基于25年甚长基线干涉测量数据的类星体S5 1928+738中尺度喷流的旋转超大质量黑洞双星特征 显示英文标题

标题： Signatures of a spinning supermassive black hole binary on the mas-scale jet of the quasar S5 1928+738 based on 25 years of VLBI data

摘要： 在之前的工作中，我们已经通过双黑洞系统的喷流特性识别出了主黑洞的自旋。通过对类星体 S5 1928+738 在$15$-GHz 频率下于$43$个观测时段（时间范围为$1995.96$至$2013.06$）的甚长基线阵列（VLBA）观测数据进行分析，我们表明内区（$<2$毫角秒）喷流对称轴的倾角变化自然可以分解为周期性和单调性两部分贡献。前者是由开普勒轨道演化引起的，而后者被解释为喷流辐射黑洞的自旋-轨道进动的特征。 本文中，我们通过纳入新的$15$-GHz VLBA观测数据重新分析了类星体S5 1928+738，这些观测数据扩展至$29$个额外的历元，时间范围在$2013.34$到$2020.89$之间。 扩展的数据集证实了我们的先前发现，并且这些发现进一步得到了喷流流量密度变化的支持。 通过应用一种改进的喷流进动模型，该模型能够处理与双超大质量黑洞系统轨道角动量任意自旋取向相关的$\kappa$情况，我们估计了双黑洞的质量比为$\nu=0.21\pm0.04$，对于$\kappa=0$（即 当自旋方向垂直于轨道平面时）以及作为 $\nu=0.32\pm0.07$对于$\kappa=\pi/2$（即 当自旋位于轨道平面内时）。 我们更精确地估计了自旋进动速度，将其不确定性从$(-0.05\pm0.02)^\circ\,\mathrm{yr}^{-1}$减半到 $(-0.04\pm0.01)^\circ\,\mathrm{yr}^{-1}$。 显示英文摘要

摘要： In a previous work, we have identified the spin of the dominant black hole of a binary from its jet properties. Analysing Very Long Baseline Array (VLBA) observations of the quasar S5~1928+738, taken at $15$-GHz during $43$ epochs between $1995.96$ and $2013.06$, we showed that the inclination angle variation of the inner ($<2$~mas) jet symmetry axis naturally decomposes into a periodic and a monotonic contribution. The former emerges due to the Keplerian orbital evolution, while the latter is interpreted as the signature of the spin-orbit precession of the jet emitting black hole. In this paper, we revisit the analysis of the quasar S5~1928+738 by including new $15$-GHz VLBA observations extending over $29$ additional epochs, between $2013.34$ and $2020.89$. The extended data set confirms our previous findings which are further supported by the flux density variation of the jet. By applying an enhanced jet precession model that can handle arbitrary spin orientations $\kappa$ with respect to the orbital angular momentum of a binary supermassive black hole system, we estimate the binary mass ratio as $\nu=0.21\pm0.04$ for $\kappa=0$ (i.e. when the spin direction is perpendicular to the orbital plane) and as $\nu=0.32\pm0.07$ for $\kappa=\pi/2$ (i.e. when the spin lies in the orbital plane). We estimate more precisely the spin precession velocity, halving its uncertainty from $(-0.05\pm0.02)^\circ\,\mathrm{yr}^{-1}$ to $(-0.04\pm0.01)^\circ\,\mathrm{yr}^{-1}$.