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>ON THE RADIO POLARIZATION SIGNATURE OF EFFICIENT AND INEFFICIENT PARTICLE ACCELERATION IN SUPERNOVA REMNANT SN?1006
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ON THE RADIO POLARIZATION SIGNATURE OF EFFICIENT AND INEFFICIENT PARTICLE ACCELERATION IN SUPERNOVA REMNANT SN?1006
Radio polarization observations provide essential information on the degree of order and orientation of magnetic fields, which themselves play a key role in the particle acceleration processes that take place in supernova remnants (SNRs). Here we present a radio polarization study of SN?1006, based on combined Very Large Array and Australia Telescope Compact Array observations at 20?cm that resulted in sensitive images with an angular resolution of 10 arcsec. The fractional polarization in the two bright radio and X-ray lobes of the SNR is measured to be 0.17, while in the southeastern sector, where the radio and non-thermal X-ray emission are much weaker, the polarization fraction reaches a value of 0.6 ± 0.2, close to the theoretical limit of 0.7. We interpret this result as evidence of a disordered, turbulent magnetic field in the lobes, where particle acceleration is believed to be efficient, and a highly ordered field in the southeast, where the acceleration efficiency has been shown to be very low. Utilizing the frequency coverage of our observations, an average rotation measure of ~12 rad m–2 is determined from the combined data set, which is then used to obtain the intrinsic direction of the magnetic field vectors. While the orientation of magnetic field vectors across the SNR shell appear to be radial, a large fraction of the magnetic vectors lie parallel to the Galactic plane. Along the highly polarized southeastern rim, the field is aligned tangent to the shock, and therefore also nearly parallel to the Galactic plane. These results strongly suggest that the ambient field surrounding SN?1006 is aligned with this direction (i.e., from northeast to southwest) and that the bright lobes are due to a polar cap geometry. Our study establishes that the most efficient particle acceleration and generation of magnetic turbulence in SN?1006 is attained for shocks in which the magnetic field direction and shock normal are quasi-parallel, while inefficient acceleration and little to no generation of magnetic turbulence are obtained for the quasi-perpendicular case.
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机译：无线电极化观测提供了有关磁场的顺序和方向的基本信息，它们本身在超新星残余（SNR）中发生的粒子加速过程中起着关键作用。在这里，我们基于20厘米处的甚大阵列和澳大利亚望远镜紧凑阵列的组合观测结果，对SN？1006进行了无线电极化研究，得出的敏感图像的角分辨率为10 arcsec。在SNR的两个明亮的无线电波和X射线波瓣中，偏振度分数为0.17，而在东南部门，X射线和非热X射线辐射要弱得多，偏振度分数为0.6±0.2，接近理论极限0.7。我们将这个结果解释为叶瓣中紊乱的湍流磁场（据信粒子加速是有效的）和东南部高度有序磁场（证据表明加速效率很低）的证据。利用我们观测的频率范围，从组合数据集中确定约12 rad m-2的平均旋转量度，然后将其用于获得磁场矢量的本征方向。尽管跨SNR壳的磁场矢量的方向看起来是径向的，但大部分磁矢量平行于银河平面。沿着高度极化的东南边缘，磁场与激波切线对齐，因此也几乎平行于银河平面。这些结果有力地表明，SN 1006周围的环境场与此方向一致（即从东北到西南），并且明亮的波瓣归因于极帽的几何形状。我们的研究表明，对于磁场方向和法线准平行的冲击，在SN？1006中获得了最有效的粒子加速和磁湍流的产生，而对于磁场冲击和法线准平行的冲击，则获得了无效的加速和几乎没有磁湍流的产生。准垂直情况。
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