Freely Expanding Knots of X-Ray-emitting Ejecta in Kepler’s Supernova Remnant
Freely Expanding Knots of X-Ray-emitting Ejecta in Kepler’s Supernova Remnant
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DOI：
10.3847/1538-4357/aa8305
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发表时间：
2017-07
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通讯作者：
Toshiki Sato;J. Hughes
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作者：
Toshiki Sato;J. Hughes
我们报告测量自行，径向速度，和元素组成的14个紧凑的X射线明亮的结在开普勒的超新星遗迹（SNR）使用档案钱德拉数据。速度最高的节既有大的自行（μ = 0.“11-0.”14 yr−1），也有高的径向速度（v = 8700- 10，020 km s−1）。对于这些节点，估计的空间速度（9100 km s−1 <$v3D <$10，400 km s−1）类似于超新星（SNe）Ia中接近最大光的典型Si速度。高速喷出物结只出现在特定的位置，并从形态和运动学不同于其余的喷出物。五节的自行外推回到开普勒的信噪比的年龄一致的中心位置。这个新的运动学中心与先前的测定结果吻合得很好，但受系统误差的影响较小，并表示遗迹中几个突出结构的高度对称性。这五个结的膨胀率接近自由膨胀率（膨胀指数为0.75 μ m × 1.0），我们认为这表明它们要么是在爆炸中形成的，具有高密度对比度（超过周围密度的100倍），要么是它们在周围介质中通过相对低密度的区域（nH < 0.1 cm−3）传播。X射线光谱分析表明，未减速结具有高的Si和S丰度，较低的Fe丰度，和非常低的O丰度，指向起源于部分Si燃烧区，这发生在超新星Ia模型的爆炸白色矮星的外层。其他结显示出较低的速度和膨胀指数与减速喷出物结或周围介质中的特征一致。我们对爆炸地点的新的精确定位具有明确的位置不确定性，允许在非传统的单简并超新星Ia情景下搜索微弱的幸存供体星的区域大大减少;由于搜索区域缺乏明亮的恒星，传统情景仍然被排除在外。
We report measurements of proper motion, radial velocity, and elemental composition for 14 compact X-ray-bright knots in Kepler’s supernova remnant (SNR) using archival Chandra data. The knots with the highest speed show both large proper motions (μ ∼ 0.″11–0.″14 yr−1) and high radial velocities (v ∼ 8700–10,020 km s−1). For these knots the estimated space velocities (9100 km s−1 ≲ v3D ≲ 10,400 km s−1) are similar to the typical Si velocity seen in supernovae (SNe) Ia near maximum light. High-speed ejecta knots appear only in specific locations and are morphologically and kinematically distinct from the rest of the ejecta. The proper motions of five knots extrapolate back over the age of Kepler’s SNR to a consistent central position. This new kinematic center agrees well with previous determinations, but is less subject to systematic errors and denotes a location about which several prominent structures in the remnant display a high degree of symmetry. These five knots are expanding at close to the free expansion rate (expansion indices of 0.75 ≲ m ≲ 1.0), which we argue indicates either that they were formed in the explosion with a high density contrast (more than 100 times the ambient density) or that they have propagated through regions of relatively low density (nH < 0.1 cm−3) in the ambient medium. X-ray spectral analysis shows that the undecelerated knots have high Si and S abundances, a lower Fe abundance, and very low O abundance, pointing to an origin in the partial Si-burning zone, which occurs in the outer layer of the exploding white dwarf for models of SNe Ia. Other knots show lower speeds and expansion indices consistent with decelerated ejecta knots or features in the ambient medium overrun by the forward shock. Our new accurate location for the explosion site has well-defined positional uncertainties, allowing for a great reduction in the area to be searched for faint surviving donor stars under non-traditional single-degenerate SNe Ia scenarios; because of the lack of bright stars in the search area the traditional scenario remains ruled out.