X-rays from Saturn: A study with XMM-Newton and Chandra
X-rays from Saturn: A study with XMM-Newton and Chandra
复制标题
DOI：
10.1051/0004-6361/200913110
复制
发表时间：
2009-11
期刊：
影响因子：
--
通讯作者：
G. Branduardi‐Raymont;A. Bhardwaj;R. Elsner;P. Rodriguez
中科院分区：
文献类型：
--
作者：
G. Branduardi‐Raymont;A. Bhardwaj;R. Elsner;P. Rodriguez
的目标。我们以一种新颖的方式利用x射线数据来研究土星及其环境，通过对迄今为止所有的行星x射线观测进行系统和统一的光谱分析。我们介绍了最近的两次（2005年）xmm -牛顿对土星的观测结果，以及对早先一次（2002年）xmm -牛顿档案观测和2003年和2004年钱德拉三次观测的重新分析。虽然xmm -牛顿望远镜的分辨率不能让我们在空间上分辨出行星盘和环对x射线通量的贡献，但我们可以通过光谱分析估计它们的强度和它们多年来的演变，并将它们与钱德拉望远镜观测到的结果进行比较。用平均温度为0.5 keV的光学薄日冕模型很好地拟合了x射线发射光谱。在0.53 keV附近加入荧光氧发射线，可显著改善拟合。根据先前的报告，我们将日冕成分解释为行星盘的辐射，由太阳x射线在土星高层大气中的散射产生，而这条线源于土星环。在2002-2005年期间，随着太阳活动衰减到目前太阳周期的最小值，圆盘x射线发射的强度下降。通过比较盘x射线辐射和氧谱线的相对通量，我们认为谱线强度不像盘通量那样随时间变化。我们考虑了这条线起源的可能的替代方案。研究了太阳活动与土星盘x射线辐射强度之间的关系，并与木星的x射线辐射强度进行了比较。我们还讨论了土星上明显缺乏x射线极光；通过比较土星与木星的极光产生相关的参数，我们得出结论，土星的x射线极光很可能没有被探测到，因为它们低于目前地球上天文台的灵敏度阈值。对天王星和海王星进行类似的比较也会得出同样令人失望的结论，这可能也适用于计划中的下一代国际x射线天文台。推进这项研究的下一步只能通过对行星的原位x射线观测来实现。
Aim. We approach the study of Saturn and its environment in a novel way using X-ray data, by making a systematic and uniform spectral analysis of all the X-ray observations of the planet to date.Methods. We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra.Results. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at similar to 0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period 2002-2005, following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn; by comparing the planet's parameters relevant to aurora production with those of Jupiter we conclude that Saturnian X-ray aurorae are likely to have gone undetected because they are below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion, which is likely to hold true also with the planned next generation International X-ray Observatory. The next step in advancing this research can only be realised with in-situ X-ray observations at the planets.