SHEAR ACCELERATION IN EXPANDING FLOWS
SHEAR ACCELERATION IN EXPANDING FLOWS
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DOI：
10.3847/1538-4357/833/1/34
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发表时间：
2016-11
期刊：
影响因子：
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通讯作者：
F. Rieger;P. Duffy
中科院分区：
文献类型：
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作者：
F. Rieger;P. Duffy
剪切流自然会发生在天体物理环境和持续的非热费米型粒子加速的潜在地点。在这里，我们研究了扩展相对论流出以促进高能带电粒子加速到更高能量的效率。为此，在解析处理的基础上推导出了渐变剪切加速度系数。这些结果适用于活动星系核的相对论喷流的背景。研究了各种锥形流型(即，幂定律、高斯、费米-狄拉克)的加速时间尺度，并与相应的辐射和非辐射损失时间尺度进行了比较。结果表明，相对论剪切流能够将宇宙线提升到极高的能量。另一方面，有效的电子加速需要弱磁场，因此可能伴随着粒子能量的延迟开始，并影响整体喷流外观(例如，核心、脊线和肢体亮化)。
Shear flows are naturally expected to occur in astrophysical environments and potential sites of continuous non-thermal Fermi-type particle acceleration. Here we investigate the efficiency of expanding relativistic outflows to facilitate the acceleration of energetic charged particles to higher energies. To this end, the gradual shear acceleration coefficient is derived based on an analytical treatment. The results are applied to the context of the relativistic jets from active galactic nuclei. The inferred acceleration timescale is investigated for a variety of conical flow profiles (i.e., power law, Gaussian, Fermi–Dirac) and compared to the relevant radiative and non-radiative loss timescales. The results exemplify that relativistic shear flows are capable of boosting cosmic-rays to extreme energies. Efficient electron acceleration, on the other hand, requires weak magnetic fields and may thus be accompanied by a delayed onset of particle energization and affect the overall jet appearance (e.g., core, ridge line, and limb-brightening).