红外回波揭示Cas A超新星的激波爆发
Infrared Echoes Reveal the Shock Breakout of the Cas A Supernova
摘要：
（凝聚态）-斯皮策卫星在Cas A超新星遗迹周围偶然发现的红外回波为天文学家提供了一个独特的机会来研究回波物质的性质以及产生这些回波的爆发的历史和性质。位于距离SN ~15弧分范围内的所有回波都是由位于爆炸源正后方160 lyr（对应于残骸采用年龄的一半）距离处的尘埃热辐射延迟到达造成的。回波的光谱与一般漫射星际介质（ISM）的光谱不同，揭示了热硅酸盐颗粒，这些颗粒要么被随机加热到超过~150 K的温度，要么在该值的平衡温度下辐射。我们表明，超新星的光学光变曲线不能产生这样的光谱，因此不能产生回波。相反，我们发现，回波产生的强烈和短暂的爆发的极紫外-紫外辐射的光度约1.5E11 Lsun。回波云中红外发射区的平均H柱密度约为5E 17 cm-2。以约1 d的爆发时间给出约200 cm-3的云密度，典型的密集红外卷云。
英文摘要：
(Condensed form) - The serendipitous discovery of infrared echoes around the supernova remnant of Cas A by the Spitzer satellite has provided astronomers with a unique opportunity to study the properties of the echoing material and the history and nature of the outburst that generated these echoes. All the echoes located within a distance of ~15 arcmin from the SN are caused by the delayed arrival of thermal emission from dust located at a distance of 160 lyr (corresponding to half the adopted age of the remnant) directly behind the origin of the explosion. The spectra of the echoes are distinct from that of the general diffuse interstellar medium (ISM) revealing hot silicate grains that are either stochastically heated to temperatures in excess of ~150 K, or radiating at an equilibrium temperature of this value. We show that the optical light curve from the supernova, is not capable of producing such spectra, and could therefore not have given rise to the echoes. Instead, we find that the echoes were generated by an intense and short burst of EUV-UV radiation with a luminosity of ~ 1.5E11 Lsun. The average H-column density of the IR emitting region in the echoing clouds is about 5E17 cm-2. Taking a burst time of ~1 d gives a cloud density of ~200 cm-3, typical of dense IR cirrus.
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