The cosmic-ray content of the Orion-Eridanus superbubble
The cosmic-ray content of the Orion-Eridanus superbubble
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DOI：
10.1051/0004-6361/201937205
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发表时间：
2020-01
影响因子：
6.5
通讯作者：
T. Joubaud;I. Grenier;J. Casandjian;T. Tolksdorf;R. Schlickeiser
中科院分区：
文献类型：
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作者：
T. Joubaud;I. Grenier;J. Casandjian;T. Tolksdorf;R. Schlickeiser
目标。附近的猎户座-仙女座超级气泡，是在几百万年前由多颗超新星吹起的，很可能产生了宇宙射线。它的湍流介质仍然被巨大的恒星风所激发，它可以在局部影响宇宙射线的传输。宇宙射线和星际气体相互作用产生的γ辐射可以用来比较超级气泡和太阳附近其他区域的宇宙射线光谱。它可以揭示超级气泡中过去和现在的恒星活动引起的GeV到TeV宇宙射线的光谱变化。方法。我们利用费米大面积望远镜（LAT）在0.25-63 GeV能量范围内的10年数据，研究了银河系低纬度超泡的近端（Eridanus）。我们模拟了在这个方向发现的云的不同气相（原子气相、分子气相、暗气相和电离气相）中产生的γ射线的空间和光谱分布。该模型包括其他非气体成分来匹配数据。结果。我们发现沿外边缘和超级气泡内部壳层的气体的γ射线发射光谱与在太阳附近测量的平均光谱是一致的。它也与在太阳系中直接测量到的宇宙射线光谱相一致。这种同质性要求对最近的超新星率进行详细的评估，并对超级气泡中目前的大质量恒星风进行普查，以便估计宇宙射线产生的时代和速度，并限制可能导致这种同质性和很少再加速的传输条件。我们还发现了重要的证据，表明位于超级气泡外的弥漫原子云，位于银道平面以下200-250个百分点的高度，其宇宙射线通量低34%，但粒子能量分布与本地相同。超级gev宇宙射线应该可以自由地穿过这样的光和漫射卷云，而不会有明显的损失或光谱扭曲。我们初步提出宇宙射线的损失与穿过卷云的磁力线的方向有关，根据普朗克的尘埃偏振数据，磁力线指向晕。最后，我们将目前的辐射率测量值与之前在太阳周围获得的估计值结合起来，以显示当地宇宙射线通量如何随着银河系高度而减少，并将这一趋势与模型预测进行比较。
Aims. The nearby Orion-Eridanus superbubble, which was blown by multiple supernovae several million years ago, has likely produced cosmic rays. Its turbulent medium is still energised by massive stellar winds and it can impact cosmic-ray transport locally. The γ radiation produced in interactions between cosmic rays and interstellar gas can be used to compare the cosmic-ray spectrum in the superbubble and in other regions near the Sun. It can reveal spectral changes induced in GeV to TeV cosmic rays by the past and present stellar activity in the superbubble. Methods. We used ten years of data from the Fermi Large Area Telescope (LAT) in the 0.25–63 GeV energy range to study the closer (Eridanus) end of the superbubble at low Galactic latitudes. We modelled the spatial and spectral distributions of the γ rays produced in the different gas phases (atomic, molecular, dark, and ionised) of the clouds found in this direction. The model included other non-gaseous components to match the data. Results. We found that the γ-ray emissivity spectrum of the gas along the outer rim and in a shell inside the superbubble is consistent with the average spectrum measured in the solar neighbourhood. It is also consistent with the cosmic-ray spectrum directly measured in the Solar System. This homogeneity calls for a detailed assessment of the recent supernova rate and current census of massive stellar winds in the superbubble in order to estimate the epoch and rate of cosmic-ray production and to constrain the transport conditions that can lead to such homogeneity and little re-acceleration. We also found significant evidence that a diffuse atomic cloud lying outside the superbubble, at a height of 200–250 pc below the Galactic plane, is pervaded by a 34% lower cosmic-ray flux, but with the same particle energy distribution as the local one. Super-GeV cosmic rays should freely cross such a light and diffuse cirrus cloud without significant loss or spectral distorsion. We tentatively propose that the cosmic-ray loss relates to the orientation of the magnetic field lines threading the cirrus, which point towards the halo according to the dust polarisation data from Planck. Finally, we gathered the present emissivity measurements with previous estimates obtained around the Sun to show how the local cosmic-ray flux decreases with Galactic height and to compare this trend with model predictions.