超新星SN2008D/XT080109和SN2007uy的同时偏振监测：从尘埃中分离几何
Simultaneous polarization monitoring of supernovae SN2008D/XT080109 and SN2007uy: isolating geometry from dust
摘要：
可能存在一个连续的爆炸性恒星死亡的多样性，从普通的SNe到相对论性超新星与长时间的伽玛射线暴，正在激烈的辩论。在这种情况下，与XT 080109相关的SN 2008 D可能代表一个典型病例，因为它可能是一个潜在的临界事件。主要目的是通过SN 2008 D的线偏振演化来推断其几何信息。我们还报告了SN 2007 uy的极化演化，并讨论了主机ISM对XT的属性。最终的目标是比较的偏振特性，因此两个SNe的几何形状，这同时在NGC 2770发光。这一幸运的巧合使我们有机会同时观察两个SNe，最重要的是，使用相同的仪器设置。观察持续74.9天，从XT后3.6天开始，分布在11次访视中。此外，我们还在毫米范围内进行了观察，以确定主导偏振。我们报告了SN 2008 D在几个时期的正线性偏振检测，其水平为~1%，SN 2007 uy为~1.5%。SN 2007 uy显示出恒定的偏振，这可以用主星际偏振加上天平面上的恒定偏心率膨胀来描述。对SN 2008 D斯托克斯参数分布的统计分析表明，它可能表现出内在的可变偏振分量。假设SN 2007 uy偏振是恒定的，我们发现，本征SN 2008 D偏振的演变可以解释为一个非球面轴对称展开与可变偏心。即使我们对SN 2007 uy不做任何假设，我们也会得到相同的结果，尽管显著性水平较低。我们认为，至少投影，如果不是内在的，两个SNe的几何形状可能不同。
英文摘要：
The possible existence of a continuum encompassing the diversity of explosive stellar deaths,ranging from ordinary SNe to relativistic hypernovae associated with long duration GRBs, is under intense debate. In this context, SN2008D associated with XT080109 could represent a paradigmatic case, since it might exemplify a potential borderline event. The main aim is to infer geometric information of SN2008D through the evolution of its linear optical polarization. We also report the polarization evolution of SN2007uy, and discuss the properties of the host ISM towards the XT. The final goal is to compare the polarization properties, and hence the geometries of both SNe, which shone contemporaneously in NGC2770. This fortunate coincidence brought us the opportunity to observe both SNe simultaneously, and most importantly, with identical instrumental setups. The observations span 74.9 days, starting 3.6 days after the XT and are distributed in 11 visits. In addition we performed observations in the mm range in order to identify the dominant polarization. We report positive linear polarization detections at several epochs for SN2008D at a level of ~1% and at ~1.5% for SN2007uy. SN2007uy shows constant polarization, which could be described by the host interstellar polarization plus a constant eccentricity expansion on the sky plane. A statistical analysis of the distribution of the SN2008D Stokes parametres suggests that it could show an intrinsic variable polarization component. Assuming the SN2007uy polarization is constant, we find that the evolution of the intrinsic SN2008D polarization could be explained by an aspherical axisymmetric expansion with variable eccentricity. We come to the same result even if we make no assumption on SN2007uy, although at a lower significance level. We suggest that at least the projected, if not the intrinsic, geometries of both SNe could differ.
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