Nature2014-06-26 1:46 PM

Cassiopeia A:一次非对称爆炸的残留体 Asymmetries in core-collapse supernovae from maps of radioactive 44Ti in CassiopeiaA

论文摘要 

对恒星核心坍缩事件的大多数模拟都表明,这些爆炸是非对称的,但所导致的形状在不同模型中则有所不同。Brian Grefenstette等人分析了Cassiopeia A(一个年轻的核心坍缩残留体)中放射性钛-44的分布,将其作为爆炸非对称性的一个代理指标。他们报告,Cassiopeia A的无激波内部的非均匀分布程度要大于从一次球形爆炸所预期的程度,但也没有按照一次高度双极爆炸所预期的那么显著。根据这些发现,本文作者得出结论认为,Cassiopeia A核心坍缩爆炸这种爆炸类型介于非对称性的两个极端之间。

Abstract 

Asymmetry is required by most numerical simulations of stellar core-collapse explosions, but the form it takes differs significantly among models. The spatial distribution of radioactive 44Ti, synthesized in an exploding star near the boundary between material falling back onto the collapsing core and that ejected into the surrounding medium, directly probes the explosion asymmetries. CassiopeiaA is a young, nearby, core-collapse remnant from which 44Ti emission has previously been detected but not imaged. Asymmetries in the explosion have been indirectly inferred from a high ratio of observed 44Ti emission to estimated 56Ni emission, from optical light echoes, and from jet-like features seen in the X-ray and optical ejecta. Here we report spatial maps and spectral properties of the 44Ti in Cassiopeia A. This may explain the unexpected lack of correlation between the 44Ti and iron X-ray emission, the latter being visible only in shock-heated material. The observed spatial distribution rules out symmetric explosions even with a high level of convective mixing, as well as highly asymmetric bipolar explosions resulting from a fast-rotating progenitor. Instead, these observations provide strong evidence for the development of low-mode convective instabilities in core-collapse supernovae.

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