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arXiv 2102.06093astro-ph.GA
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Cas A超新星遗迹的射电和X射线自谱和交叉角功率谱

The auto and cross angular power spectrum of the Cas A supernova remnant in radio and X-ray

Preetha Saha, Somnath Bharadwaj, Susmita Chakravorty, Nirupam Roy, Samir Choudhuri, Hans Moritz Günther, Randall K. Smith

摘要:

壳型超新星遗迹(SNR)Cas A在几乎所有的角尺度上都表现出结构。以往的研究表明,射电辐射的角功率谱$(C_{\ell})$是一个破幂律,符合MHD湍流。在对应于壳体厚度的角尺度上,已经确定了从2D到3D湍流的过渡。或者,这也可以解释为二维逆级联驱动的能量注入从结激波相互作用。在这里,我们提出$C_{\ell}$测量档案VLA $5$ GHz(C波段)的数据,和钱德拉X射线数据的能量范围${\rm A}=0.6-1.0 \, \, {\rm keV}$和${\rm B} =4.2-6.0 \, \, {\rm keV}$,这两个都是连续占主导地位。不同的辐射都是底层等离子体的波动,也可能是磁场的波动,我们希望它们是相关的。我们使用不同发射之间的交叉$C_{\ell}$来量化这一点。我们发现X射线B与射电和X射线A都有很强的相关性,而X射线A与射电的相关性很弱。这支持了这样一种观点,即X射线A主要是热韧致辐射,而X射线B是热韧致辐射和非热同步辐射的复合辐射。这里测量的各种$C_{\ell}$都显示出破幂律行为。然而,这些斜率通常比无线电中的斜率要浅,并且断裂的位置也对应于较小的角度尺度。这些发现提供了有关湍流性质和Cas A发射机制的观测输入。

英文摘要:

The shell type supernova remnant (SNR) Cas A exhibits structures at nearly all angular scales. Previous studies show the angular power spectrum $(C_{\ell})$ of the radio emission to be a broken power law, consistent with MHD turbulence. The break has been identified with the transition from 2D to 3D turbulence at the angular scale corresponding to the shell thickness. Alternatively, this can also be explained as 2D inverse cascade driven by energy injection from knot-shock interactions. Here we present $C_{\ell}$ measured from archival VLA $5$GHz (C band) data, and Chandra X-ray data in the energy ranges ${\rm A}=0.6-1.0 \, \, {\rm keV}$ and ${\rm B} =4.2-6.0 \, \, {\rm keV}$, both of which are continuum dominated. The different emissions all trace fluctuations in the underlying plasma and possibly also the magnetic field, and we expect them to be correlated. We quantify this using the cross $C_{\ell}$ between the different emissions. We find that X-ray B is strongly correlated with both radio and X-ray A, however X-ray A is only very weakly correlated with radio. This supports a picture where X-ray A is predominantly thermal bremsstrahlung whereas X-ray B is a composite of thermal bremsstrahlung and non-thermal synchrotron emission. The various $C_{\ell}$ measured here, all show a broken power law behaviour. However, the slopes are typically shallower than those in radio and the position of the break also corresponds to smaller angular scales. These findings provide observational inputs regarding the nature of turbulence and the emission mechanisms in Cas A.

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