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arXiv 0806.1589astro-ph
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Ic型SN 2007 gr的旋光光谱和非球面度

Optical Spectropolarimetry and Asphericity of Type Ic SN 2007gr

Masaomi Tanaka, Koji S. Kawabata, Keiichi Maeda, Takashi Hattori, Ken'ichi Nomoto

摘要:

利用斯巴鲁望远镜对Ic型超新星(SN)2007 gr进行了最大亮度后21天(爆发后37天)的分光偏振观测。在Ca II IR三重态的吸收特征处观察到高达~3%的非零偏振。如果我们假设连续偏振具有单个偏振角来估计星际偏振(ISP)分量,则连续光的偏振为~0.5%。这表明SN光球投射到天空的轴比与1相差约10%。在钙II吸收的偏振角几乎对齐的连续光。这些功能可以理解的模型,其中一个双极爆炸与扁圆光球被认为是从轻微的离轴方向和爆炸合成的钙附近的极区模糊的光起源周围的SN光球的短轴。然而,由于ISP的不确定性,偏振数据也可以用几乎球对称的光球和clustrial Ca II分布的模型来解释。

英文摘要:

We present optical spectropolarimetric observations of Type Ic supernova (SN) 2007gr with Subaru telescope at 21 days after the maximum brightness (~37 days after the explosion). Non-zero polarization as high as ~3% is observed at the absorption feature of Ca II IR triplet. The polarization of the continuum light is ~0.5% if we estimate the interstellar polarization (ISP) component assuming that the continuum polarization has a single polarization angle. This suggests that the axis ratio of the SN photosphere projected to the sky is different from unity by ~10%. The polarization angle at the Ca II absorption is almost aligned to that of the continuum light. These features may be understood by the model where a bipolar explosion with an oblate photosphere is viewed from the slightly off-axis direction and explosively synthesized Ca near the polar region obscures the light originated around the minor axis of the SN photosphere. Given the uncertainty of the ISP, however, the polarization data could also be interpreted by the model with an almost spherically symmetric photosphere and a clumpy Ca II distribution.

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