Relativistic Thermal Emission from Accretion Disks in Kerr-MOG Spacetimes
Kerr-MOG时空中吸积盘的相对论热辐射
Cheng Liu, Xu-fan Hu, Yosuke Mizuno, Tao Zhu
AI总结 研究标量-张量-矢量引力(MOG)中矢量场对Kerr-MOG黑洞吸积盘热连续谱的影响,发现第五种力使ISCO外移、峰值温度降低并软化热谱,且与自旋降低效应类似,需结合铁线反射谱区分。
Comments 16pages, 11 figures. Accepted for publication in ApJ
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在标量-张量-矢量引力(STVG,也称为MOG)中,一个质量矢量场$ϕ_μ$产生排斥性的第五种力,使旋转黑洞具有引力电荷$Q \propto \sqrtα\\,M$,通过单个变形参数$α$修改近视界几何。我们研究这种矢量场耦合如何印迹在Kerr-MOG黑洞的几何薄、光学厚吸积盘的热连续谱发射上。通过重新推导Kerr-MOG时空的最内稳定圆轨道(ISCO)、Novikov-Thorne辐射通量、相对论能量偏移和零测地线结构,我们使用专用的\textsc{xspec}谱模型(\texttt{kmspec})计算了广泛自旋、倾角和第五种力强度下的完全相对论性盘谱。我们发现,第五种力电荷将ISCO向外推,降低峰值盘温度,并系统性地使热连续谱相对于相同自旋的Kerr黑洞对应物变软,且在高观测倾角下偏差放大。由此产生的谱修改密切模仿纯Kerr黑洞框架中自旋的降低,表明来自例如铁线反射谱的独立自旋测量对于区分矢量场贡献是不可或缺的。当$α= 0$时,所有结果恢复标准Kerr黑洞预测,并且该模型通过独立解析和数值基准验证达到机器精度。应用于LMC X-1的69.6 ks \textit{XMM-Newton}观测,在90%置信度下得到$α< 0.044$,与Kerr度规和广义相对论一致。
In Scalar-Tensor-Vector Gravity (STVG, also known as MOG), a massive vector field $ϕ_μ$ generates a repulsive fifth force that endows rotating black holes with a gravitational charge $Q \propto \sqrtα\,M$, modifying the near-horizon geometry through a single deformation parameter $α$. We investigate how this vector-field coupling imprints itself on the thermal continuum emission of geometrically thin, optically thick accretion disks in the Kerr-MOG black hole. By re-deriving the innermost stable circular orbit (ISCO), the Novikov-Thorne radiative flux, the relativistic energy shift, and the null geodesic structure for the Kerr-MOG spacetime, we compute fully relativistic disk spectra across a broad range of spins, inclinations, and fifth-force strengths using a dedicated \textsc{xspec} spectral model (\texttt{kmspec}). We find that the fifth-force charge pushes the ISCO outward, lowers the peak disk temperature, and systematically softens the thermal continuum relative to its Kerr black hole counterpart at the same spin, with the deviation amplified at high observer inclinations. The resulting spectral modification closely mimics a reduction of spin in the pure Kerr black hole framework, indicating that independent spin measurements from, e.g., iron-line reflection spectroscopy are indispensable for disentangling the vector-field contribution. All results recover the standard Kerr black hole predictions when $α= 0$, and the model is validated against independent analytic and numerical benchmarks to machine precision. Application to a 69.6~ks \textit{XMM-Newton} observation of LMC~X-1 yields $α< 0.044$ at 90\% confidence, consistent with the Kerr metric and general relativity.