SN 2006 aj在9.6天时的分光偏振法
Spectropolarimetry of SN 2006aj at 9.6 days
摘要：
分光偏振观测技术已被用于直接测量超新星（SNe）、伽马射线暴（GRB）和X射线闪光（XRF）的不对称性。我们希望确定是否存在与GRB和XRF相关的SNe中的非轴向不对称性，在这些情况下，考虑到射流轴和对称轴与视线的特定对齐。我们进行了光谱偏振与甚大望远镜（VLT）FORS 1仪器的类型Ic SN 2006 aj，与XRF 060218，在V波段最大值在9.6休息帧天后，检测的XRF。由于仅在3个延迟板角度下进行观察，假设$U$斯托克斯参数的仪器特征校正与$Q$测量的校正相同，则数据被减少。我们发现SN 2006 aj在对应于某些谱线吸收最小值的波长处具有高度偏振性，特别是在4200 nm处观察到的O I 7774 nm和Fe II，偏振度为3%。星际极化的值并没有很好地受到这些观测的约束，考虑到在6000- 6500光年之间观测到的低极化，SN的全球不对称性为$\lesssim 15%$。O I和Fe II线共享不同于Ca II的偏振角。SN 2006 aj比其他与GRB和XRF相关的SNe表现出更高程度的线偏振。与谱线相关的偏振意味着这些元素相对于彼此和相对于视线的显著不对称。这与与GRB/XRF相关的SN的标准图像相反，其中SN的对称轴与GRB喷流轴和视线对齐。
英文摘要：
The observational technique of spectropolarimetry has been used to directly measure the asymmetries of Supernovae (SNe), Gamma-Ray Bursts (GRBs) and X-Ray Flashes (XRFs). We wish to determine if non-axial asymmetries are present in SNe that are associated with GRBs and XRFs, given the particular alignment of the jet axis and axis of symmetry with the line of sight in these cases. We performed spectropolarimetry with the Very Large Telescope (VLT) FORS1 instrument of the Type Ic SN 2006aj, associated with the XRF 060218, at V-band maximum at 9.6 rest frame days after the detection of the XRF. Due to observations at only 3 retarder plate angles, the data were reduced assuming that the instrumental signature correction for the $U$ Stokes parameter was identical to the correction measured for $Q$. We find SN 2006aj to be highly polarized at wavelengths corresponding to the absorption minima of certain spectral lines, particularly strong for O I 7774Åand Fe II, observed at 4200Åwith a polarization 3%. The value of the Interstellar Polarization is not well constrained by these observations and, considering the low polarization observed between 6000-6500Å, the global asymmetry of the SN is $\lesssim 15%$. O I and Fe II lines share a polarization angle that differs from Ca II. SN 2006aj exhibits a higher degree of line polarization than other SNe associated with GRBs and XRFs. The polarization associated with spectral lines implies significant asymmetries of these elements with respect to each other and to the line of sight. This is contrary to the standard picture of SNe associated with GRBs/XRFs, where the axis of symmetry of the SN is aligned with the GRB jet axis and the line of sight.
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