SPATIALLY RESOLVED SPECTROSCOPY OF A BALMER-DOMINATED SHOCK IN THE CYGNUS LOOP: AN EXTREMELY THIN COSMIC-RAY PRECURSOR?
SPATIALLY RESOLVED SPECTROSCOPY OF A BALMER-DOMINATED SHOCK IN THE CYGNUS LOOP: AN EXTREMELY THIN COSMIC-RAY PRECURSOR?
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DOI：
10.3847/2041-8205/819/2/l32
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发表时间：
2016-02
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通讯作者：
S. Katsuda;K. Maeda;Y. Ohira;Y. Yatsu;K. Mori;W. Aoki;K. Morihana;J. Raymond;P. Ghavamian;Jaejoon Lee;J. Shimoda;R. Yamazaki
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作者：
S. Katsuda;K. Maeda;Y. Ohira;Y. Yatsu;K. Mori;W. Aoki;K. Morihana;J. Raymond;P. Ghavamian;Jaejoon Lee;J. Shimoda;R. Yamazaki
我们提出了高分辨率的长狭缝光谱的巴尔默为主的冲击在天鹅座圈的东北翼与斯巴鲁高色散摄谱仪。通过沿着激波法线设置狭缝角，我们研究了从激波前到激波后Hα线的通量和轮廓的变化，空间分辨率为0.4 × 10 ~（15）cm。Hα谱线轮廓可以用激波前扩散区的窄（28.9 ± 0.7 km s-1）高斯分布来表示，即，一个光致电离的前兆，以及在激波本身的窄（33.1 ± 0.2 km s−1）加宽（130-230 km s−1）高斯。我们发现，在激波处的一个未分辨薄层（距离为540 pc，104 × 1015 cm）中，窄分量的宽度突然增加到33.1 ± 0.2 km s-1，或者如果我们消除来自光电离前体的投射发射，则为38.8 ± 0.4 km s-1。我们表明，突然变宽可以最好地解释加热通过阻尼阿尔文波在一个薄的宇宙射线（CR）的前体，虽然其他可能性并没有完全排除。Cygnus Loop（软γ射线发射体）中CR前体的厚度比Tycho Knot g（硬γ射线发射体）中的CR前体的厚度薄一个数量级，这可能是由于两个源之间加速粒子的能量分布不同造成的。在这种情况下，系统的研究可能会揭示CR前体的厚度和CR能量分布的硬度之间的正相关性。
We present high-resolution long-slit spectroscopy of a Balmer-dominated shock in the northeastern limb of the Cygnus Loop with the Subaru high dispersion spectrograph. By setting the slit angle along the shock normal, we investigate variations of the flux and profile of the Hα line from preshock to postshock regions with a spatial resolution of ∼4 × 1015 cm. The Hα line profile can be represented by a narrow (28.9 ± 0.7 km s−1) Gaussian in a diffuse region ahead of the shock, i.e., a photoionization precursor, and narrow (33.1 ± 0.2 km s−1) plus broad (130–230 km s−1) Gaussians at the shock itself. We find that the width of the narrow component abruptly increases up to 33.1 ± 0.2 km s−1, or 38.8 ± 0.4 km s−1 if we eliminate projected emission originating from the photoionization precursor, in an unresolved thin layer (≲4 × 1015 cm at a distance of 540 pc) at the shock. We show that the sudden broadening can be best explained by heating via damping of Alfvén waves in a thin cosmic-ray (CR) precursor, although other possibilities are not fully ruled out. The thickness of the CR precursor in the Cygnus Loop (a soft gamma-ray emitter) is an order of magnitude thinner than that in Tycho’s Knot g (a hard gamma-ray emitter), which may be caused by the different energy distribution of accelerated particles between the two sources. In this context, systematic studies might reveal a positive correlation between the thickness of the CR precursor and the hardness of the CR energy distribution.