A time-dependent particle acceleration and emission model: understanding particle spectral evolution and blazar flares
A time-dependent particle acceleration and emission model: understanding particle spectral evolution and blazar flares
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与时间相关的粒子加速和发射模型：了解粒子光谱演化和耀斑耀斑
DOI：
10.1093/mnras/staa2919
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Bai J. M.
中科院分区：
文献类型：
--
作者：
Zheng Y. G.;Kang S. J.;Yang C. Y.;Bai J. M.
耀变体的喷流以其多波长的耀斑和快速的极端变化而闻名；然而，关于这些发射性质的光谱和时间变化的物理过程，仍然有一些重要的未解之谜。本文建立了耀变体发射光谱随时间变化的粒子演化模型。在模型中，我们引入了随时间变化的电场和磁场，它们始终包含输运方程中相关物理量的可变性。电子分布的演化由一个广义输运方程进行数值求解，该方程包含描述静电、一阶和二阶\emph{费米}加速、平流和空间扩散引起的粒子逃逸以及同步加速器发射和同步加速器和外部环境光子场的逆康普顿散射引起的能量损失的项。我们发现耀变体的光曲线轮廓与随时间变化的电场和磁场导致的粒子光谱演化相一致，而不是加速或冷却过程的影响。该模型能够在合理的物理参数假设下同时解释BL Lac天体Mrk 421的能谱和光曲线轮廓的变化。结果表明，耀变体喷流耗散区的磁场演化可以解释这种变化。
The jets of blazars are renowned for their multi-wavelength flares and rapid extreme variability; however, there are still some important unanswered questions about the physical processes responsible for these spectral and temporal changes in emission properties. In this paper, we develop a time-dependent particle evolution model for the time-varying emission spectrum of blazars. In the model, we introduce time-dependent electric and magnetic fields, which consistently include the variability of relevant physical quantities in the transport equation. The evolution on the electron distribution is numerically solved from a generalized transport equation that contains the terms describing the electrostatic, first-order and second-order \emph{Fermi} acceleration, escape of particles due to both advection and spatial diffusion, as well as energy losses due to the synchrotron emission and inverse-Compton scattering of both synchrotron and external ambient photon fields. We find that the light curve profiles of blazars are consistent with the particle spectral evolution resulting from time-dependent electric and magnetic fields, rather than the effects of the acceleration or the cooling processes. The proposed model is able to simultaneously account for the variability of both the energy spectrum and the light curve profile of the BL Lac object Mrk 421 with reasonable assumptions about the physical parameters. The results strongly indicate that the magnetic field evolution in the dissipated region of a blazar jet can account for the variabilities.