On the Origin of Radial Magnetic Fields in Young Supernova Remnants
On the Origin of Radial Magnetic Fields in Young Supernova Remnants
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DOI：
10.1086/178059
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发表时间：
1996-05
期刊：
影响因子：
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通讯作者：
Byung-Il. Jun;M. Norman
中科院分区：
文献类型：
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作者：
Byung-Il. Jun;M. Norman
我们用三维数值MHD模拟的方法研究了年轻超新星残骸的瑞利-泰勒不稳定性。计算是在球面极坐标（r, θ， ϕ）中进行的，使用移动网格技术，使我们能够精细地解决壳。三维结果比二维结果显示混合区域的湍流（复杂）结构更多，并且发现不稳定性使反向激波前缘变形。计算斯托克斯参数（I， Q和U）来研究残余的无线电特性。总强度图显示了两个不同的区域（内层和外层）。由于瑞利-泰勒不稳定性，内壳看起来复杂而动荡，表现出环状结构和羽状，而外壳由于受到均匀的环境磁场的冲击而暗淡而层流。内壳与年轻信噪比主壳中观测到的射电结构相似，这证明了瑞利-泰勒不稳定性是年轻信噪比的一个持续过程。当只考虑不稳定性产生的磁场的特殊分量时，内射电壳的极化b向量优先径向化，其分数极化率约为20% ~ 50%，高于观测值。分数极化在湍流内壳处最低，向外增大，这是几何效应的结果。发现极化强度与总强度相关。我们证明，如果放大场足够强，湍流区的极化强度可以优于激波均匀场的极化强度。因此，我们得出结论，瑞利-泰勒不稳定性可以解释年轻超新星残骸主壳中的主要径向磁场。然而，由于激波压缩，由于该区域没有被瑞利-泰勒不稳定性混合，因此外暗壳显示出主要的切向场方向，这与观测结果相反。因此，需要另一种机制来产生外激波磁场的径向分量，我们建议是块状介质模型。
We study the radio emission from young supernova remnants by means of three-dimensional numerical MHD simulations of the Rayleigh-Taylor instability in the shell of the remnant. The computation is carried out in spherical polar coordinates (r, θ, ϕ) by using a moving grid technique that allows us to resolve the shell finely. The three-dimensional result shows more turbulent (complex) structures in the mixing region than the two-dimensional result, and the instability is found to deform the reverse shock front. Stokes parameters (I, Q, and U) are computed to study the radio properties of the remnant. The total intensity map shows two distinctive regions (inner and outer shells). The inner shell appears to be complex and turbulent, exhibiting loop structures and plumes as a result of the Rayleigh-Taylor instability, while the outer shell is faint and laminar because of the shocked uniform ambient magnetic fields. The inner shell resembles the observed radio structure in the main shell of young SNRs, which is evidence that the Rayleigh-Taylor instability is an ongoing process in young SNRs. When only the peculiar components of the magnetic fields generated by the instability are considered, the polarization B-vector in the inner radio shell is preferentially radial with about 20%-50% of fractional polarization, which is higher than the observed value. The fractional polarization is lowest in the turbulent inner shell and increases outward, which is attributed to the geometric effect. The polarized intensity is found to be correlated with the total intensity. We demonstrate that the polarized intensity from the turbulent region can dominate over the polarized intensity from the shocked uniform fields if the amplified field is sufficiently strong. Therefore, we conclude that the Rayleigh-Taylor instability can explain the dominant radial magnetic field in the main shell of young supernova remnants. However, the outer faint shell shows a dominant tangential field orientation due to the shock-compression because this region is not mixed by the Rayleigh-Taylor instability, which is contrary to observations. Therefore, another mechanism is necessary to produce the radial components of the magnetic field at the outer shock, which we suggest to be a clumpy medium model.