发表机构
JILA, University of Colorado and National Institute of Standards and Technology; Department of Astrophysical and Planetary Sciences, University of Colorado; The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University; Center for Integrated Plasma Studies, Physics Department, University of Colorado; Center for Computational Astrophysics, Flatiron Institute（科罗拉多大学JILA与美国国家标准与技术研究院; 科罗拉多大学天体物理与行星科学系; 特拉维夫大学雷蒙德和贝弗利萨克勒物理与天文学学院; 科罗拉多大学物理系综合等离子体研究中心; 平顿研究所计算天体物理学中心）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
通过首次GRMHD模拟揭示条带化喷流从发射到耗散的全局演化，发现迷你喷流电磁加速与电流片形成机制，耗散率可达坡印廷功率的数十%，可解释BL Lac耀变体超光速特征。
AI 中文摘要
条带化喷流以极性交替的磁主导区域为特征，能够在条带之间形成的全局电流片中实现快速磁能耗散，因此被视为耀变体观测到的高能辐射和伽马射线暴瞬时辐射的可行来源。我们进行了首次全局轴对称广义相对论磁流体动力学（GRMHD）模拟，追踪条带化喷流从发射（通过将极性交替的极向磁环吸积到旋转黑洞上）到在大距离处能量耗散的演化过程。每个磁环的吸积都会发射出一股携带螺旋磁场的坡印廷通量主导的迷你喷流，其极性继承自该磁环，这些迷你喷流的集合构成了喷流核心。相对论性核心被一个非相对论性鞘层包围，该鞘层由先前发射的迷你喷流在嵌套结构中返回的场线组成。高效的迷你喷流发射要求吸积盘中的极向磁环在靠近黑洞处（$r \lesssim 50\\,r_g$）形成；否则，它们会因湍流而失去相干性。一旦发射，迷你喷流会像稳态喷流一样进行电磁加速，只要与喷流轴保持横向因果接触，洛伦兹因子就随喷流横截面半径线性增加。当两个携带相反方向磁场的尾随迷你喷流接触时，会形成电流片。早期电流片的形成得益于迷你喷流的纵向膨胀，这种膨胀由内部压力驱动，发生在流动变为超快磁声速之前。我们在模拟盒子（$10^4\\,r_g$）内测量到，在观测者参考系中，能量耗散率占喷流坡印廷功率的百分之几十。我们的结果可以解释BL Lac型耀变体中观测到的明亮超光速特征。
英文摘要
Striped jets, characterized by magnetically dominated regions with alternating polarity, can enable fast magnetic energy dissipation in global current sheets formed in between the stripes, and are thus considered as a viable source for the high-energy emission observed in blazars and gamma-ray burst prompt emission. We perform the first global axisymmetric GRMHD simulations that follow the evolution of striped jets from their launching, by accretion of poloidal magnetic loops with alternating polarity onto a spinning black-hole, to their energy dissipation at large distances. The accretion of each loop launches a Poynting-flux-dominated mini-jet carrying a helical magnetic field whose polarity is inherited from the loop, and the collection of which forms the jet core. The relativistic core is surrounded by a non-relativistic sheath composed of returning fieldlines from previously launched mini-jets in a nested configuration. Efficient mini-jet launching requires poloidal loops in the accretion disk to form close to the black hole ($r \lesssim 50\,r_g$); otherwise, they lose coherency due to turbulence. Once launched, the mini-jets accelerate electromagnetically, similar to steady-state jets, with the Lorentz factor increasing linearly with the jet cross-sectional radius as long as lateral causal contact with the jet axis is maintained. Current sheets form when two trailing mini-jets carrying oppositely directed magnetic fields come into contact. Early sheet formation is facilitated by the longitudinal expansion of the mini-jets, driven by internal pressure before the flow becomes super-fast-magnetosonic. We measure an energy dissipation rate of a few tens of percent of the jet Poynting power in the observer frame, within our simulation box of $10^4\,r_g$. Our results can account for the bright superluminal features observed in BL Lac type blazars.
Comments19 pages, 15 figures
