Cassiopeia A reveals past interaction with circumstellar shell
Cassiopeia A reveals past interaction with circumstellar shell
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仙后座 A 揭示了过去与星周壳的相互作用
DOI：
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
G. Peres
中科院分区：
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作者：
S. Orlando;A. Wongwathanarat;H. Janka;M. Miceli;S. Nagataki;M. Ono;F. Bocchino;J. Vink;D. Milisavljevic;D. Patnaude;G. Peres
上下文超新星遗迹（SNR）仙后座A（Cas A）的观测显示，反向激波中存在显著的不对称性，这无法用描述遗迹通过祖先星星的球对称风膨胀的模型来解释。目标。我们调查是否可以解释所观察到的反向冲击的不对称性的一个巨大的不对称壳的星周介质的过去的相互作用的Cas A。方法.我们进行了三维（3D）（磁）流体动力学模拟，描述了从SN爆炸到其与大规模拱壳相互作用的残余演化。初始条件（在恒星表面激波爆发后不久）由3D中微子驱动的SN模型提供，其形态与Cas A非常相似（Wongwathanarat et al. 2017）。SNR模拟涵盖了2000年的演变，包括所有必要的物理过程来描述残留壳层的相互作用。我们探索了壳层的参数空间，寻找一组参数，这些参数能够在10350年的年龄产生类似于在Cas A中观察到的反向冲击不对称性。结果如果壳层在西北（NW）的（蓝移的）近侧不对称，则残骸与壳层的相互作用可以与反向激波中观察到的不对称相匹配。根据我们最喜欢的模型，炮弹很薄（厚度σ = 0.02 pc），距离爆炸中心的半径rsh = 1.5 pc。反激波在Cas A时代表现出以下不对称性：（1）在观测坐标系中，反激波在NW区向内移动，而在其它区域向外移动：（2）反激波的几何中心相对于正激波的几何中心向NW方向偏移0.1pc; iii）西北地区的反向激波增强了非热辐射，因为，在那里，喷出物进入反向激波的相对速度（4000 - 7000 km/s）高于其他区域（低于2000 km/s）。结论.在Cas A的反向激波中观察到的主要不对称性可以被解释为超新星爆发后180年至240年之间发生的遗迹与不对称致密星周壳层相互作用的特征。我们认为，壳层很可能是在核心坍缩前10年发生的祖星星大规模喷发的结果。我们估计Msh的壳层总质量为2.6 M。
Context. Observations of the supernova remnant (SNR) Cassiopeia A (Cas A) show significant asymmetries in the reverse shock that cannot be explained by models describing a remnant expanding through a spherically symmetric wind of the progenitor star. Aims. We investigate whether a past interaction of Cas A with a massive asymmetric shell of the circumstellar medium can account for the observed asymmetries of the reverse shock. Methods. We performed three-dimensional (3D) (magneto)-hydrodynamic simulations that describe the remnant evolution from the SN explosion to its interaction with a massive circumstellar shell. The initial conditions (soon after the shock breakout at the stellar surface) are provided by a 3D neutrino-driven SN model whose morphology closely resembles Cas A (Wongwathanarat et al. 2017). The SNR simulations cover ≈ 2000 years of evolution and include all physical processes necessary to describe the remnant-shell interaction. We explored the parameter space of the shell, searching for a set of parameters able to produce reverse shock asymmetries at the age of ≈ 350 years analogous to those observed in Cas A. Results. The interaction of the remnant with the shell can match the observed asymmetries in the reverse shock if the shell was asymmetric with the densest portion in the (blueshifted) nearside to the northwest (NW). According to our favorite model, the shell was thin (thickness σ ≈ 0.02 pc) with a radius rsh ≈ 1.5 pc from the center of the explosion. The reverse shock shows the following asymmetries at the age of Cas A: i) it moves inward in the observer frame in the NW region, while it moves outward in other regions; ii) the geometric center of the reverse shock is offset to the NW by ≈ 0.1 pc from the geometric center of the forward shock; iii) the reverse shock in the NW region has enhanced nonthermal emission because, there, the ejecta enter the reverse shock with a higher relative velocity (between 4000 and 7000 km s) than in other regions (below 2000 km s). Conclusions. The main asymmetries observed in the reverse shock of Cas A can be interpreted as signatures of the interaction of the remnant with an asymmetric dense circumstellar shell that occurred between ≈ 180 and ≈ 240 years after the SN event. We suggest that the shell was, most likely, the result of a massive eruption from the progenitor star that occurred about 10 years prior to core-collapse. We estimate a total mass of the shell of Msh ≈ 2.6 M⊙.