The Milky Way hosts on average a few supernova explosions per century, yet in the past millennium only five supernovae have been identified confidently in the historical record. This deficit of naked-eye supernovae is at least partly due to dust extinction in the Galactic plane. We explore this effect quantitatively, developing a formalism for the supernova probability distribution in space and on the sky, accounting for dust and for the observer’s flux limit. We then construct a fiducial axisymmetric model for the spatial supernova and dust densities, featuring an exponential dependence on galactocentric radius and height, with core-collapse events in a thin disc and Type Ia events including a thick disc component. When no flux limit is applied, our model predicts that on the sky, supernovae are intrinsically concentrated in the Galactic plane, with Type Ia events extending to higher latitudes. We then apply a flux limit and include dust effects, to predict the sky distribution of historical supernovae. We use well-observed supernovae as light-curve templates, and introduce naked-eye discovery criteria. The resulting sky distributions are strikingly inconsistent with the locations of confident historical supernovae, none of which lie near our model’s central peaks. Indeed, SN 1054 lies off the plane almost exactly in the anticentre, and SN 1181 is in the second Galactic quadrant. We discuss possible explanations for these discrepancies. We calculate the percentage of all supernovae bright enough for historical discovery: $\simeq 13{{\ \rm per\ cent}}$ of core-collapse and $\simeq 33{{\ \rm per\ cent}}$ of Type Ia events. Using these and the confident historical supernovae, we estimate the intrinsic Galactic supernova rates, finding general agreement with other methods. Finally, we urge searches for supernovae in historical records from civilizations in the Southern hemisphere.

中文翻译：

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见证历史：肉眼银河系超新星的天空分布、可探测性和比率

银河系平均每个世纪都会发生几次超新星爆炸，但在过去的千年中，历史记录中只有五颗超新星被确定地确定。肉眼超新星的这种不足至少部分是由于银河平面中的尘埃灭绝。我们定量地探索了这种效应，为空间和天空中的超新星概率分布开发了一种形式，考虑了尘埃和观察者的通量限制。然后，我们为空间超新星和尘埃密度构建了一个基准轴对称模型，该模型具有对星系中心半径和高度的指数依赖性，薄盘中的核心坍塌事件和包括厚盘组件的 Ia 型事件。当没有应用通量限制时，我们的模型预测，在天空中，超新星本质上集中在银河平面，Ia 型事件延伸到更高的纬度。然后，我们应用通量限制并包括尘埃效应，来预测历史超新星的天空分布。我们使用观测良好的超新星作为光曲线模板，并引入肉眼发现标准。由此产生的天空分布与确信的历史超新星的位置惊人地不一致，这些超新星都没有位于我们模型的中心峰附近。事实上，SN 1054 几乎正好位于反中心，而 SN 1181 位于银河系的第二象限。我们讨论了这些差异的可能解释。我们计算了所有足以历史发现的超新星的百分比：$\simeq 13{{\ \rm per\ cent}}$ of core-collapse and $\simeq 33{{\rm per\ cent}}$ of type IA事件。使用这些和自信的历史超新星，我们估计了固有的银河超新星率，发现与其他方法基本一致。最后，我们敦促在南半球文明的历史记录中寻找超新星。