Deep XMM-Newton Observations Reveal the Origin of Recombining Plasma in the Supernova Remnant W44
Deep XMM-Newton Observations Reveal the Origin of Recombining Plasma in the Supernova Remnant W44
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DOI：
10.3847/1538-4357/ab6987
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发表时间：
2019-12
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通讯作者：
H. Okon;Takaaki Tanaka;H. Uchida;H. Yamaguchi;T. Tsuru;M. Seta;Randall K. Smith;S. Yoshiike;S. Orlando;F. Bocchino;M. Miceli
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作者：
H. Okon;Takaaki Tanaka;H. Uchida;H. Yamaguchi;T. Tsuru;M. Seta;Randall K. Smith;S. Yoshiike;S. Orlando;F. Bocchino;M. Miceli
最近的 X 射线研究揭示了十几个混合形态 (MM) 超新星遗迹 (SNR) 中的过度电离重组等离子体。然而，过度电离的物理过程尚未完全了解。在这里，我们使用来自深度观测的 XMM-Newton 数据报告了 W44（超电离 MM SNR 之一）X 射线发射的空间分辨光谱，目的是澄清超电离的物理起源。我们发现在与致密分子云相互作用的区域中实现了低电子温度和低复合时间尺度的结合。此外，从有和没有分子云的每个区域都获得了电子温度和复合时间尺度之间的明显反相关性。如果等离子体因 W44 冲击波撞击致密云层而通过热传导快速冷却而过度电离，则结果可以得到很好的解释。鉴于其他一些过度电离的信噪比显示绝热膨胀是快速冷却的主要驱动因素的证据，我们的新结果表明这两个过程都可能导致信噪比的过度电离，其中主导通道取决于进化阶段。
Recent X-ray studies have revealed overionized recombining plasmas in a dozen mixed-morphology (MM) supernova remnants (SNRs). However, the physical process of the overionization has not yet been fully understood. Here we report on spatially resolved spectroscopy of X-ray emission from W44, one of the overionized MM SNRs, using XMM-Newton data from deep observations, with the aim of clarifying the physical origin of the overionization. We find that combination of low electron temperature and low recombination timescale is achieved in the region interacting with dense molecular clouds. Moreover, a clear anticorrelation between the electron temperature and the recombination timescale is obtained from each of the regions with and without the molecular clouds. The results are well explained if the plasma was overionized by rapid cooling through thermal conduction with the dense clouds hit by the blast wave of W44. Given that a few other overionized SNRs show evidence for adiabatic expansion as the major driver of the rapid cooling, our new result indicates that both processes can contribute to overionization in SNRs, with the dominant channel depending on the evolutionary stage.