探测Centaurus A喷流中的各向异性粒子加速和边缘增亮
Probing anisotropic particle acceleration and limb-brightening in Centaurus A's jet
AI总结：
本文通过3D GRMHD模拟和GRRT计算，研究Cen A喷流的边缘增亮结构，并发现磁性冻结盘结合各向异性粒子分布可解释EHT观测结果，同时推断Cen A黑洞阴影将在3 THz频率下可观测。
摘要：
相对论喷流是宇宙中最引人注目的天体之一，近年来高分辨率VLBI观测，包括全球毫米波VLBI阵列和事件视界望远镜（EHT），能够解析其接近喷流发射点的结构。这些观测揭示了Centaurus A（Cen A）、M 87和3C 84的强烈边缘增亮喷流结构。因此，问题在于哪种物理机制能产生边缘增亮结构，以及这种结构是否常见于低亮度活动星系核（LLAGN）在大视向角下。因此，作为初步研究，我们旨在建模Cen A的EHT观测。我们进行了一个三维双温度广义相对论磁流体力学（GRMHD）模拟，研究吸积超大质量黑洞（SMBH）和喷流发射的动力学，并通过广义相对论辐射传输（GRRT）计算计算了连接发射，考虑可能的辐射粒子分布各向异性。为了调整我们的模拟以适应Cen A的EHT观测，我们进行了傅里叶平面的贝叶斯拟合。我们发现，磁性冻结盘（MADs）的GRMHD模拟结合沿磁场方向各向异性发射的粒子分布，参数化为值η=0.07，能够模拟最近的Cen A EHT观测。此外，我们提取出黑洞质量M_BH=6×10^7 M_太阳和视向角θ=72°。我们获得的模型可以再现EHT和阿塔卡马大毫米波/亚毫米波阵列（ALMA）观测在总和极化发射中的关键特征。最后，我们预测Cen A的黑洞阴影将在约3 THz频率下可观测。
英文摘要：
Relativistic jets are among the most fascinating objects in the Universe, and recent high-resolution Very Long Baseline Interferometric (VLBI) observations, including the Global mm-VLBI Array and the Event Horizon Telescope (EHT), are able to resolve their structure close to their launching site. These observations reveal strongly limb-brightened jet structures for Centaurus A (Cen A), M 87 and 3C 84. Thus, the question arises which physical mechanism can generate the limb-brightened structure, and if this structure is common for jets from low-luminosity active galactic nuclei (LLAGN) seen under large viewing angles. Therefore, as a pilot study, we aim to model the EHT observations of Cen A. We performed a 3D two-temperature general-relativistic magnetohydrodynamic (GRMHD) simulation of an accreting supermassive black hole (SMBH) and jet launching to study the plasma dynamics and computed the connected emission via general relativistic radiative transfer (GRRT) calculations considering possible anisotropies in the distribution of the radiating particles. In order to adjust our simulations to the EHT observations of Cen A, we carried out a Bayesian fitting in the Fourier plane. We find that GRMHD simulations of magnetically arrested disks (MADs) combined with anisotropically emitting particle distributions along the direction of the magnetic field, parametrized by a value $η=0.07$, are able to mimic the recent EHT observations of Cen A. In addition, we extracted a black hole mass of $M_\mathrm{BH} = 6\times10^7 M_\odot$ and a viewing angle of $\vartheta=72°$. Our obtained model can reproduce key features of the EHT and Atacama Large Millimeter/submillimeter Array (ALMA) observations in total and polarized emission. Finally, we predict that the black hole shadow in Cen A will be observable at a frequency of $\sim$ 3 THz.
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