Discovery of Year-scale Time Variability from Thermal X-Ray Emission in Tycho’s Supernova Remnant
Discovery of Year-scale Time Variability from Thermal X-Ray Emission in Tycho’s Supernova Remnant
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DOI：
10.3847/1538-4357/ac94cf
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
M. Matsuda;H. Uchida;Takaaki Tanaka;H. Yamaguchi;T. Tsuru
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作者：
M. Matsuda;H. Uchida;Takaaki Tanaka;H. Yamaguchi;T. Tsuru
粒子加热机制对于理解超新星遗迹中的激波物理至关重要。然而，到目前为止，关于热化粒子的时间变化的信息很少。在这里，我们提出了在2000-2015年期间获得的Tycho SNR的Chandra数据中发现的逐渐变亮的热X射线发射的发现。发射呈现出一个结状的特征（Knot 1），直径为1.04 pc，位于西北边缘，我们在2008年哈勃太空望远镜拍摄的光学图像中也发现了局部Hα细丝。太阳丰度的模型再现了Knot 1的光谱，表明Knot 1起源于星际介质;这是在第谷SNR中发现的第一个来自扫掠气体的热X射线发射。我们的光谱分析表明，在2000年至2015年期间，Knot 1的电子温度从10.30 keV增加到10.69 keV。这些结果使我们归因于时间可变的排放到一个小的密集的团块最近加热的前向激波在位置的结1。为了重现这些数据，激波下游的电子-质子温度比（β 0 <$Te/Tp）被限制为m e /m p ≤ β 0 ≤ 0. 15，这表明无碰撞电子加热效率与Tycho和其他高激波速度SNR的Hα观测结果是一致的。
Mechanisms of particle heating are crucial to understanding the shock physics in supernova remnants (SNRs). However, there has been little information on time variabilities of thermalized particles so far. Here, we present a discovery of a gradually brightening thermal X-ray emission found in the Chandra data of Tycho’s SNR obtained during 2000–2015. The emission exhibits a knot-like feature (Knot1) with a diameter of ≃0.04 pc located in the northwestern limb, where we also find localized Hα filaments in an optical image taken with the Hubble Space Telescope in 2008. The model with the solar abundance reproduces the spectra of Knot1, suggesting that Knot1 originates from the interstellar medium; this is the first detection of thermal X-ray emission from swept-up gas found in Tycho’s SNR. Our spectral analysis indicates that the electron temperature of Knot1 has increased from ∼0.30 to ∼0.69 keV within the period between 2000 and 2015. These results lead us to ascribe the time-variable emission to a small dense clump recently heated by the forward shock at the location of Knot1. The electron-to-proton temperature ratio immediately downstream of the shock (β 0 ≡ T e /T p ) is constrained to be m e /m p ≤ β 0 ≤ 0.15 to reproduce the data, indicating the collisionless electron heating with efficiency is consistent with previous Hα observations of Tycho and other SNRs with high shock velocities.