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arXiv 0812.3823astro-ph
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1/4 keV能区太阳风电荷转移X射线辐射:低Z时局部泡状热气体的推论

The solar wind charge-transfer X-ray emission in the 1/4 keV energy range: inferences on Local Bubble hot gas at low Z

D. Koutroumpa, R. Lallement, J. C. Raymond, V. Kharchenko

摘要:

我们目前的计算日光层SWCX发射光谱和它们的贡献在ROSAT 1/4千电子伏波段。我们比较了我们的结果与软X射线扩散背景(SXRB)的发射在前面的378个确定的阴影区域在ROSAT全天巡天(斯诺登等。2000年)。这一前景成分主要归因于所谓的局部气泡(LB)的热气体,这是一个围绕太阳约50 - 150 pc的不规则形状的空腔,应该包含约10^6 K的等离子体。我们的研究结果表明,从日光层的SWCX发射是明亮的,足以占大多数低银河纬度方向的前景发射,其中LB是最少的扩展。在银纬30度以上的大部分方向上,日球SWCX强度明显小于实测值。然而,SWCX R2/R1的波段比与银河系中心方向的数据略有不同,在银河系反中心方向的观测比值最小。假设SWCX和热气体发射都存在,并且它们的相对贡献随方向而变化,我们测试了一系列温度范围从10^5到10^6.5 K的热等离子体光谱,并寻找SWCX光谱和热发射的组合,这些光谱和热发射与观察到的强度和能带比相匹配,同时与O VI发射测量兼容。在碰撞平衡模型的框架下,对于太阳丰度,我们得到的热气体温度和辐射测量的范围不能再现威斯康星C/B带比。我们强调需要额外的原子数据,描述一致的EUV和X射线光子光谱的电荷交换发射较重的太阳风离子。

英文摘要:

We present calculations of the heliospheric SWCX emission spectra and their contributions in the ROSAT 1/4 keV band. We compare our results with the soft X-ray diffuse background (SXRB) emission detected in front of 378 identified shadowing regions during the ROSAT All-Sky Survey (Snowden et al. 2000). This foreground component is principally attributed to the hot gas of the so-called Local Bubble (LB), an irregularly shaped cavity of ~50-150 pc around the Sun, which is supposed to contain ~10^6 K plasma. Our results suggest that the SWCX emission from the heliosphere is bright enough to account for most of the foreground emission towards the majority of low galactic latitude directions, where the LB is the least extended. In a large part of directions with galactic latitude above 30deg the heliospheric SWCX intensity is significantly smaller than the measured one. However, the SWCX R2/R1 band ratio differs slightly from the data in the galactic center direction, and more significantly in the galactic anti-centre direction where the observed ratio is the smallest. Assuming that both SWCX and hot gas emission are present and their relative contributions vary with direction, we tested a series of thermal plasma spectra for temperatures ranging from 10^5 to 10^6.5 K and searched for a combination of SWCX spectra and thermal emission matching the observed intensities and band ratios, while simultaneously being compatible with O VI emission measurements. In the frame of collisional equilibrium models and for solar abundances, the range we derive for hot gas temperature and emission measure cannot reproduce the Wisconsin C/B band ratio. We emphasize the need for additional atomic data, describing consistently EUV and X-ray photon spectra of the charge-exchange emission of heavier solar wind ions.

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