Observation and origin of non-thermal hard X-rays from Jupiter
Observation and origin of non-thermal hard X-rays from Jupiter
复制标题
木星非热硬 X 射线的观测和起源
作者：
K. Mori;C. Hailey;G. Bridges;S. Mandel;Amani Garvin;B. Grefenstette;W. Dunn;B. Hord;G. Branduardi‐Raymont;J. Clarke;C. Jackman;M. Nynka;L. Ray
电子在地球上被各种各样的波散射或随机过程加速1，2，产生高达~1 MeV的硬非热X射线韧致辐射（参考文献3，4），并为地球上各种类型的极光提供动力。尽管木星的磁场比地球的磁场大一个数量级，但太空望远镜之前只能检测到高达~7 keV的X射线（参考文献5）。根据木星极光X射线产生的理论模型6 -8，在~2-7 keV波段的X射线发射被解释为热（由麦克斯韦-玻尔兹曼分布特征的电子产生）韧致辐射5，9。在这里，我们报告的观测硬X射线在8-20千电子伏波段的木星极光，获得与努斯塔X射线天文台。X射线符合平坦的幂律模型，斜率为0.60 ± 0.22-非热硬X射线韧致辐射的光谱特征。我们确定的电子通量和光谱形状在千电子伏到兆电子伏的能量范围内使用同时代的原位测量朱诺号飞船的JADE和JEDI仪器。我们观察到的木星电子光谱形式以前被解释为随机加速，而不是电场的相干加速。我们重现的X射线光谱形状和近似通量观测到的努斯塔，并解释了非检测到的硬X射线的Ulysses 11，通过模拟非热人口的电子经历沉淀电子能量损失，二次电子产生和韧致辐射发射在一个模型木星大气。结果突出了地球和木星上产生硬X射线极光的过程之间的相似性，这也可能发生在土星上。木星上的努斯塔仪器探测到极光区的非热硬X射线韧致辐射。朱诺号航天器的同步原位观测证实了非热电子加速的特征，并强调了与地球极光过程的相似之处。
Electrons accelerated on Earth by a rich variety of wave-scattering or stochastic processes1,2 generate hard, non-thermal X-ray bremsstrahlung up to ~1 MeV (refs. 3,4) and power Earth’s various types of aurorae. Although Jupiter’s magnetic field is an order of magnitude larger than Earth’s, space-based telescopes have previously detected X-rays only up to ~7 keV (ref. 5). On the basis of theoretical models of the Jovian auroral X-ray production6–8, X-ray emission in the ~2–7 keV band has been interpreted as thermal (arising from electrons characterized by a Maxwell–Boltzmann distribution) bremsstrahlung5,9. Here we report the observation of hard X-rays in the 8–20 keV band from the Jovian aurorae, obtained with the NuSTAR X-ray observatory. The X-rays fit to a flat power-law model with slope of 0.60 ± 0.22—a spectral signature of non-thermal, hard X-ray bremsstrahlung. We determine the electron flux and spectral shape in the kiloelectronvolt to megaelectronvolt energy range using coeval in situ measurements taken by the Juno spacecraft’s JADE and JEDI instruments. Jovian electron spectra of the form we observe have previously been interpreted as arising in stochastic acceleration, rather than coherent acceleration by electric fields10. We reproduce the X-ray spectral shape and approximate flux observed by NuSTAR, and explain the non-detection of hard X-rays by Ulysses11, by simulating the non-thermal population of electrons undergoing precipitating electron energy loss, secondary electron generation and bremsstrahlung emission in a model Jovian atmosphere. The results highlight the similarities between the processes generating hard X-ray aurorae on Earth and Jupiter, which may be occurring on Saturn, too. Non-thermal, hard X-ray bremsstrahlung emission from auroral regions is detected at Jupiter by the NuSTAR instrument. Simultaneous in situ observations from the Juno spacecraft confirm the signatures of acceleration from non-thermal electrons and highlight the similarities with auroral processes on Earth.
Juno/JEDI 测量的木星主要极光区的沉淀电子能量通量和特征能量
DOI：
10.1029/2018ja025639
发表时间：
2018
期刊：
Space Physics
影响因子：
--
作者：
Clark G
通讯作者：
Clark G