SN 1006西北缘激波后等离子体中的温度弛豫测量
Measurement of Temperature Relaxation in the Postshock Plasma of the Northwestern Limb of SN 1006
AI总结：
为填补激波下游温度弛豫观测缺失，研究人员用Chandra观测SN 1006西北X射线纤维，分层拟合光谱发现电子温度升幅低于库仑散射预期，需其他效应解释，有望借未来X射线任务验证。
摘要：
通过无碰撞激波加热带电粒子的现象虽在宇宙中普遍存在，却是一种引人关注又令人困惑的等离子体现象。一个悬而未决的问题是，电子和离子在被加热至不同的激波后瞬时温度后，如何达到平衡状态。为填补激波下游温度弛豫过程观测信息的严重缺失，我们利用Chandra（钱德拉X射线天文台）观测了SN 1006西北部一条以热辐射为主的X射线纤维状结构。我们将该区域分为四层，每层厚度为15角秒（即0.16秒差距），并采用非平衡电离碰撞等离子体模型拟合各层光谱。研究发现，在60角秒（即0.64秒差距）的尺度上，电子温度从下游方向的0.52-0.62 keV升高至0.82-0.95 keV。该电子温度低于库仑散射导致的热弛豫过程的预期温度，说明还存在湍流导致的等离子体混合和/或投影效应等其他作用，我们希望未来的XRISM和Athena等X射线量能谱仪任务能够解决这一问题。
英文摘要：
Heating of charged particles via collisionless shocks, while ubiquitous in the universe, is an intriguing yet puzzling plasma phenomenon. One outstanding question is how electrons and ions approach an equilibrium after they were heated to different immediate-postshock temperatures. In order to fill the significant lack of observational information of the downstream temperature-relaxation process, we observe a thermal-dominant X-ray filament in the northwest of SN~1006 with Chandra. We divide this region into four layers with a thickness of 15$^{\prime\prime}$ or 0.16 pc each, and fit each spectrum by a non-equilibrium ionization collisional plasma model. The electron temperature was found to increase toward downstream from 0.52-0.62 keV to 0.82-0.95 keV on a length scale of 60 arcsec (or 0.64 pc). This electron temperature is lower than thermal relaxation processes via Coulomb scattering, requiring some other effects such as plasma mixture due to turbulence and/or projection effects, etc, which we hope will be resolved with future X-ray calorimeter missions such as XRISM and Athena.
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