标题： SN 1006 中反向激波的时间演化 显示英文标题

标题： Time Evolution of the Reverse Shock in SN 1006

摘要： 位于SN 1006遗迹之后并在其投影中心附近的Schweizer-Middleditch星，提供了通过紫外线吸收研究SN 1006壳层内的冷膨胀抛射物的机会。特别值得注意的是Si II 1260埃特征的极尖锐红端，这来自于SN 1006壳层远侧最快移动的抛射物——这些物质刚刚遇到逆向冲击波。比较2010年用COS获得的HST远紫外光谱和1999年用STIS获得的光谱，我们测量了该特征在10.5年的间隔内的变化。我们发现Si II特征的尖锐红端向蓝方向移动了0.19 +/- 0.05埃，这意味着2010年遇到逆向冲击波的物质比1999年遇到它的物质速度慢了44 +/- 11公里/秒，这一变化相当于-4.2 +/- 1.0公里/秒/年。这是对逆向冲击波长期预测的动态效应的首次观测确认：即冲击波将逐步向内穿过膨胀的超新星抛射物，并在行进过程中遇到越来越慢的物质。我们还发现，在十年期间，经过逆向冲击波的受激Si II的柱密度减少了7 +/- 2%。这种减少可能表明，在这个方向上，逆向冲击波正在穿过一个致密的硅团块，导致压力和密度的瞬变。 显示英文摘要

摘要： The Schweizer-Middleditch star, located behind the SN 1006 remnant and near its center in projection, provides the opportunity to study cold, expanding ejecta within the SN 1006 shell through UV absorption. Especially notable is an extremely sharp red edge to the Si II 1260 Angstrom feature, which stems from the fastest moving ejecta on the far side of the SN 1006 shell--material that is just encountering the reverse shock. Comparing HST far-UV spectra obtained with COS in 2010 and with STIS in 1999, we have measured the change in this feature over the intervening 10.5-year baseline. We find that the sharp red edge of the Si II feature has shifted blueward by 0.19 +/- 0.05 Angstroms, which means that the material hitting the reverse shock in 2010 was moving slower by 44 +/- 11 km/s than the material that was hitting it in 1999, a change corresponding to - 4.2 +/- 1.0 km/s/yr. This is the first observational confirmation of a long-predicted dynamic effect for a reverse shock: that the shock will work its way inward through expanding supernova ejecta and encounter ever slower material as it proceeds. We also find that the column density of shocked Si II (material that has passed through the reverse shock) has decreased by 7 +/- 2% over the ten-year period. The decrease could indicate that in this direction the reverse shock has been ploughing through a dense clump of Si,leading to pressure and density transients.