Model Dependence of XRISM Black Hole Spin Constraints in Cyg X-1
Cyg X-1中XRISM黑洞自旋约束的模型依赖性
We study the persistent black hole X-ray binary Cyg X-1, recently observed by XRISM Resolve and simultaneously by NICER and NuSTAR in its hard spectral state. We confirm the result of Draghis et al. that fits of the Resolve data alone with the simplest available relativistic reflection model, relxill, yield a black hole spin parameter close to the maximum, a<SUB>*</SUB> ≍ 0.99. However, fitting with an improved, Comptonization-based model, relxillCp, yields a low a<SUB>*</SUB> = 0. 0<SUP>+0.17</SUP>. A similarly low range is obtained with another Comptonization-based model, reflkerrD. Then fits to the combined data require two Comptonization model components but are consistent with any spin value. We conclude that the spin value of Cyg X-1 is strongly model dependent. However, low spin values are consistent with the constraints from gravitational waves. All of the models constrain the inner disk radius to be ≲10 gravitational radii, which is consistent with a recent finding of the weakness of thermal reverberation in Cyg X-1. The suggested source geometry is that of an outflowing disk corona, which was also proposed to explain the X-ray polarization observed from this source.
展开 ▾首次在XRISM高分辨率光谱中系统对比relxill与更物理的反射模型(relxillCp、reflkerrD),证实自旋测量可从~0.99降至0,低自旋解与引力波观测相符,并支持外流冕几何。
过去,基于连续谱拟合(Zhao+ 2021)和反射谱分析(Draghis+ 2025b)的方法均给出Cyg X-1的极端自旋(接近1),但这与引力波观测到的低自旋分布(The LIGO Scientific Collaboration+ 2025)形成明显矛盾。本研究利用XRISM高分辨率谱线,证明当采用包含康普顿化的反射模型(García+ 2018b、Niedźwiecki+ 2019)时,自旋参数可降至约0,揭示模型依赖性是目前自旋测量的关键系统误差。此外,限制内盘半径≲10 Rg与外流冕几何(Poutanen+ 2023;偏振证据见Krawczynski+ 2022)以及微弱的软X射线混响(Basak+ 2025)均指向一个较紧致的盘-冕结构。未来,结合更真实的吸积物理模型、多波段高能谱及改进的仪器间校准,将是弥合X射线与引力波自旋测量分歧的关键。
预印本 2026-05-23 · 接收 2026-06-26 · 刊出 2026-07-09 · 收录 2026-07-22