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arXiv 0808.0692astro-ph
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仙后座A超新星遗迹中非热X射线暗条的自行和亮度变化

Proper Motions and Brightness Variations of Nonthermal X-ray Filaments in the Cassiopeia A Supernova Remnant

Daniel J. Patnaude, Robert A. Fesen

摘要:

我们目前钱德拉ACIS X射线观测银河超新星遗迹仙后座A采取在2007年12月。将这些数据与钱德拉在2000年、2002年和2004年的观测资料相结合,我们估计残骸在最外层壳周围不同点的前向冲击速度在4200和5200 +/- 500 km/s之间。利用这些结果,结合以前对Cas A X射线辐射的分析,我们提出了一个Cas A演化的模型,发现它的膨胀很好地符合进入周风的rho_ej ~ r^{-(7-9)}喷出物轮廓。我们进一步发现,虽然在这个模型中的反向冲击波的位置是一致的,在X射线测量,为了匹配的前向冲击波的速度和半径,我们不得不假设,约30%的爆炸能量已经进入加速宇宙射线在前向冲击波。新的X射线图像还显示,一些向前的激波丝可能会发生亮度变化,就像在残骸内部投射的几个非热灯丝所看到的那样。对外部前向激波细丝和内部非热细丝的谱拟合表明,它们具有相似的谱。这与类似的通量变化一起表明,内部非热细丝可能只是投影中看到的前向激波细丝,而不是像最近提出的那样位于反向激波处。

英文摘要:

We present Chandra ACIS X-ray observations of the Galactic supernova remnant Cassiopeia A taken in December 2007. Combining these data with previous archival Chandra observations taken in 2000, 2002, and 2004, we estimate the remnant's forward shock velocity at various points around the outermost shell to range between 4200 and 5200 +/- 500 km/s. Using these results together with previous analyses of Cas A's X-ray emission, we present a model for the evolution of Cas A and find that it's expansion is well fit by a rho_ej ~ r^{-(7-9)} ejecta profile running into a circumstellar wind. We further find that while the position of the reverse shock in this model is consistent with that measured in the X-rays, in order to match the forward shock velocity and radius we had to assume that ~ 30% of the explosion energy has gone into accelerating cosmic rays at the forward shock. The new X-ray images also show that brightness variations can occur for some forward shock filaments like that seen for several nonthermal filaments seen projected in the interior of the remnant. Spectral fits to exterior forward shock filaments and interior nonthermal filaments show that they exhibit similar spectra. This together with similar flux variations suggests that interior nonthermal filaments might be simply forward shock filaments seen in projection and not located at the reverse shock as has been recently proposed.

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