标题： 双极超新星爆炸 显示英文标题

标题： Bi-polar Supernova Explosions

摘要： 我们讨论了几颗核心坍缩超新星的光学光谱偏振特性，包括SN 1996cb（IIb型）、SN 1997X（Ic型）和SN 1998S（IIn型）。 观测数据显示了几个光谱特征在0.5%到超过4%之间的偏振演化。 观测到的线偏振是超新星本身的固有性质，而非星际介质所致。 这些数据表明喷发物质的分布高度非球对称。 对于SN 1998S，在偏椭球形喷发物质以边缘视角呈现且偏振度为3%的情况下，长轴与短轴的最小比值必须大于2.5:1。 通过光谱偏振测量可以推断出IIn型超新星SN 1998S具有明确的对称轴，但IIb型事件SN 1993J和SN 1996cb似乎具有更复杂的几何结构，其偏振位置角在光谱特征中显示出更大的不规则变化；后者可能与喷发物的大尺度团块性有关。 Ic型超新星SN 1997X的观测偏振度超过5%。 数据显示了一个趋势：偏振度随包层质量减小以及喷发物内部深度增加而增大。 我们推测IIb型、Ib型和Ic型可能是从不同视角观察到的非常相似的事件。 II型爆炸的传统中微子驱动核心坍缩模型难以解释喷发物的高轴比。 高度不对称的爆炸机制，如核心坍缩期间双极喷流的形成，可能是所有核心坍缩超新星模型的必要组成部分。 显示英文摘要

摘要： We discuss the optical spectropolarimetry of several core-collapse supernovae, SN 1996cb (Type IIB), SN 1997X (Type Ic), and SN 1998S (Type IIn). The data show polarization evolution of several spectral features at levels from 0.5% to above 4%. The observed line polarization is intrinsic to the supernovae and not of interstellar origin. These data suggest that the the distribution of ejected matter is highly aspherical. In the case of SN 1998S, the minimum major to minor axis ratio must be larger than 2.5 to 1 if the polarization is 3% from an oblate spheroidal ejecta seen edge on. A well-defined symmetry axis can be deduced from spectropolarimetry for the peculiar Type IIn supernova SN 1998S but the Type IIB events SN 1993J and SN 1996cb seem to possess much more complicated geometries with polarization position angles showing larger irregular variations across spectral features; the latter may be associated with large scale clumpiness of the ejecta. The observed degree of polarization of the Type Ic SN 1997X is above 5%. The data reveal a trend that the degree of polarization increases with decreasing envelope mass and with the depth within the ejecta. We speculate that Type IIB, Type Ib, and Type Ic may be very similar events viewed from different aspect angles. The high axial ratio of the ejecta is difficult to explain in terms of the conventional neutrino driven core-collapse models for Type II explosions. Highly asymmetric explosion mechanisms such as the formation of bipolar jets during core-collapse may be a necessary ingredient for models of all core-collapse supernovae.