A study of Jupiter's aurorae with XMM-Newton
A study of Jupiter's aurorae with XMM-Newton
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DOI：
10.1051/0004-6361:20066406
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发表时间：
2007-02-01
影响因子：
6.5
通讯作者：
Cravens, T. E.
中科院分区：
文献类型：
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作者：
Branduardi-Raymont, G.;Bhardwaj, A.;Cravens, T. E.
我们对 2003 年 11 月在两次 XMM-牛顿革命中观测到的木星 X 射线（0.2-10 keV）极光发射进行了详细分析，并将其与 2003 年 4 月的早期观测进行了比较。我们发现极光中存在电子轫致辐射成分，它基本上解释了所有高于 2 keV 的 X 射线通量：它的存在已被预测，但由于缺乏而从未被检测到。以前的 X 射线任务的灵敏度。在 2003 年 11 月观测的 3.5 天内，这种轫致辐射成分的强度和光谱形状变化很大，随着通量的增加，光谱显着硬化。这种变化可能与当时发生的强烈太阳活动有关，并且可能是由木星磁层内部加速机制的变化引起的。与 2003 年 4 月一样，低于 2 keV 的极光光谱最适合由最有可能源自离子电荷交换的线发射叠加来拟合，其中 OVII 起主导作用。我们仍然无法最终确定造成最低能量线（约 0.3 keV）的离子种类，因此离子（磁层或太阳风）起源的问题仍然悬而未决。可以想象，这两种情况在一个非常复杂的行星结构中都发挥着作用。使用 XMM-牛顿反射光栅光谱仪在 0.5-1 keV 范围内获得的整个行星的高分辨率光谱清楚地将源自木星低纬度地区的发射线（主要是铁）与氧气产生的极光线分开。它们具有非常宽的机翼，这意味着速度接近 5000 km s(-1)。这样的速度与预计在木星磁层中加速沉淀和电荷交换氧离子的能量一致。总体而言，我们发现我们的测量结果与最近开发的木星极光过程模型的预测非常一致。
We present a detailed analysis of Jupiter's X-ray (0.2-10 keV) auroral emissions as observed over two XMM-Newton revolutions in Nov. 2003 and compare it with that of an earlier observation in Apr. 2003. We discover the existence of an electron bremsstrahlung component in the aurorae, which accounts for essentially all the X-ray flux above 2 keV: its presence had been predicted but never detected for lack of sensitivity of previous X-ray missions. This bremsstrahlung component varied significantly in strength and spectral shape over the 3.5 days covered by the Nov. 2003 observation, displaying substantial hardening of the spectrum with increasing flux. This variability may be linked to the strong solar activity taking place at the time, and may be induced by changes in the acceleration mechanisms inside Jupiter's magnetosphere. As in Apr. 2003, the auroral spectra below 2 keV are best fitted by a superposition of line emission most likely originating from ion charge exchange, with OVII playing the dominant role. We still cannot resolve conclusively the ion species responsible for the lowest energy lines (around 0.3 keV), so the question of the origin of the ions (magnetospheric or solar wind) is still open. It is conceivable that both scenarios play a role in what is certainly a very complex planetary structure. High resolution spectra of the whole planet obtained with the XMM-Newton Reflection Grating Spectrometer in the range 0.5-1 keV clearly separate emission lines (mostly of iron) originating at low latitudes on Jupiter from the auroral lines due to oxygen. These are shown to possess very broad wings which imply velocities of similar to 5000 km s(-1). Such speeds are consistent with the energies at which precipitating and charge exchanging oxygen ions are expected to be accelerated in Jupiter's magnetosphere. Overall we find good agreement between our measurements and the predictions of recently developed models of Jupiter's auroral processes.