Multiple Supernova Remnant Models of the Local Bubble and the Soft X-Ray Background
Multiple Supernova Remnant Models of the Local Bubble and the Soft X-Ray Background
复制标题
局部气泡和软X射线背景的多个超新星遗迹模型
DOI：
10.1086/320850
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发表时间：
2001
期刊：
影响因子：
--
通讯作者：
D. Cox
中科院分区：
文献类型：
--
作者：
Randall K. Smith;D. Cox
本文探讨了一系列的两个或三个超新星在弥漫的星际介质中可能能够产生一个长寿的热弥漫气泡的特性，如推断的本地气泡围绕太阳的可能性。多超新星遗迹的几个例子进行了探讨，能够遵循非平衡电离和尘埃破坏的一维流体代码。通过缩放参数的结果是广义的，并确定了一组输入参数，这实际上应该导致满足所有已知的约束尺寸，外部压力，外部密度，X射线表面亮度和频带比，上限的X射线发射在0.5-1千电子伏的范围内，和O VI吸收线特性的气泡。探索模型是一个独特的例子，详细的行为热星际气泡，他们的特点是相当详细。包括温度、密度和压力的分布，以及这些分布随时间的演变，膨胀和收缩过程中气泡半径的演变，观测带和特定观测线中X射线发射的演变，将X射线表面亮度归一化为半径、压力和中心温度的诊断，X射线发射率的径向依赖性，完整的X射线和EUV光谱，潜在可观察到的吸收线的等效宽度，O-VI吸收的具体特性（柱密度、质心速度、宽度）、电子柱密度、O VI、Fe X和Fe XIV的发射线强度、尘埃被破坏的程度，以及不完全的尘埃破坏对其他一切的影响。观测表明，来自局部气泡的铁的发射线很弱或不存在。这有点令人惊讶，因为即使仅通过热溅射，也预期会有相当大的晶粒破坏。这一结果与其他证据相似，即大部分铁存在于其自身的尘埃中，并且非常难以破坏。在我们的模型中，仅将铁消耗10倍，使其更容易适应X射线发射特性。成功的模型还要求热气泡内的热传导大约以其完全经典速率的一半发生。对于显著较低的热导率，温度太高而不能得到正确的光谱特性，并且在最高允许压力下密度太低而不能实现观察到的亮度。我们的基准模型假设，在300万年的时间里，太阳附近发生了三次超新星爆发，最后一次发生在几百万年前。我们表明，这种偶然事件应该是足够普遍的，提供约1的机会在30（相当大的不确定性）被发现在一个。当然，超新星发生在OB协会之外，最近在深海铁锰地壳中发现了过量的60 Fe，这可能是500万年前附近超新星的直接证据，该超新星可能是最近局部泡沫重新加热的原因。
This paper examines the possibility that a series of two or three supernovae in the diffuse interstellar medium might be capable of generating a long-lived hot diffuse bubble with characteristics like those inferred for the Local Bubble surrounding the Sun. Several examples of multiple supernova remnants are explored with a one-dimensional hydrocode able to follow the nonequilibrium ionization and dust destruction. The results are generalized via scaling parameters, and a set of input parameters are identified, which should in fact lead to a bubble satisfying all known constraints on size, external pressure, external density, X-ray surface brightness and band ratios, the upper limit to X-ray emission in the 0.5-1 keV range, and the O VI absorption line characteristics. The exploratory models are a unique example of the detailed behavior of hot interstellar bubbles, and their characteristics are presented in considerable detail. Included are the distributions of temperature, density, and pressure, as well as the evolutions of those distributions with time, the evolution of bubble radius during both expansion and contraction, the evolution of the X-ray emission in observed bands and specific observed lines, a diagnostic for normalizing the X-ray surface brightness to radius, pressure, and central temperature, the radial dependence of X-ray emissivity, the full X-ray and EUV spectrum, the equivalent widths of potentially observable absorption lines, the specific characteristics of the O VI absorption (column density, centroid velocity, width), the electron column density, the emission line intensities for O VI, Fe X, and Fe XIV, the degree to which dust can be expected to have been destroyed, and the effects of incomplete dust destruction on everything else. Observations have shown that the emission lines of iron from the Local Bubble are weak or absent. This is somewhat surprising, since considerable grain destruction is expected, even if only by thermal sputtering. The result is similar to other hints that much of the iron is in its own population of dust and is very resistant to destruction. In our models, having iron alone depleted by a factor of 10 makes it much easier to accommodate the X-ray emission characteristics. Having a successful model also requires that thermal conduction within the hot bubble occurs at roughly half of its full classical rate. For substantially lower thermal conductivity, the temperature is too high to get the spectral characteristics right, and the density is too low at the highest allowed pressure to achieve the observed brightness. Our fiducial model assumes that three supernovae took place in the vicinity of the Sun over a period of 3 million years, the last having occurred a few million years ago. We show that such accidental occurrences should be sufficiently common to provide about 1 chance in 30 (with considerable uncertainty) of being found within one. Certainly supernovae occur outside of OB associations, and direct evidence for a nearby supernova some 5 million years ago that could have been responsible for the latest reheating of the Local Bubble has recently been found in the excess abundance of 60Fe in a deep ocean ferromanganese crust.