Title: The demographics of neutron star - white dwarf mergers: rates, delay-time distributions and progenitors Show Chinese title

Title: 中子星-白矮星合并的群体统计：速率、延迟时间分布和前身天体

Abstract: The mergers of neutron stars (NSs) and white dwarfs (WDs) could give rise to explosive transients, potentially observable with current and future transient surveys. However, the expected properties and distribution of such events is not well understood. Here we characterize the rates of such events, their delay time distribution, their progenitors and the distribution of their properties. We use binary populations synthesis models and consider a wide range of initial conditions and physical processes. In particular we consider different common-envelope evolution models and different NS natal kick distributions. We provide detailed predictions arising from each of the models considered. We find that the majority of NS-WD mergers are born in systems in which mass-transfer played an important role, and the WD formed before the NS. For the majority of the mergers the WDs have a carbon-oxygen composition (60-80%) and most of the rest are with oxygen-neon WDs. The rates of NS-WD mergers are in the range of 3-15% of the type Ia supernovae (SNe) rate. Their delay time distribution is very similar to that of type Ia SNe, but slightly biased towards earlier times. They typically explode in young 0.1-1Gyr environments, but have a tail distribution extending to long, Gyrs-timescales. Models including significant kicks give rise to relatively wide offset distribution extending to hundreds of kpcs. The demographic and physical properties of NS-WD mergers suggest they are likely to be peculiar type Ic-like SNe, mostly exploding in late type galaxies. Their overall properties could be related to a class of rapidly evolving SNe recently observed, while they are less likely to be related to the class of Ca-rich SNe. Show Chinese abstract

Abstract: 中子星（NS）与白矮星（WD）的并合可能会引发爆炸性暂现源，这些暂现源可能被当前和未来的暂现巡天观测到。然而，人们对这类事件的预期性质和分布尚不完全了解。 在这里，我们描述了这类事件的发生率、延迟时间分布、它们的前身星以及其属性的分布。 我们使用双星群体合成模型，并考虑了广泛的初始条件和物理过程。 特别是，我们考虑了不同的公共包层演化模型和不同的NS产前喷动分布。 我们提供了每种模型产生的详细预测。 我们发现，大多数NS-WD并合事件诞生于质量转移起重要作用的系统中，并且WD形成的时间早于NS。 对于大多数并合事件，WD具有碳氧组成（60-80%），其余大部分是氧氖WD。 NS-WD并合的发生率处于Ia型超新星（SNe）发生率的3-15%之间。 它们的延迟时间分布非常类似于Ia型SNe，但稍微偏向较早的时间。 它们通常在年轻0.1-1Gyr的环境中爆炸，但也有一部分延伸到长时间尺度上，达到数Gyr。 包括显著喷动的模型会产生相对宽广的偏移分布，范围可达数百kpc。 NS-WD并合事件的人口统计学和物理属性表明，它们很可能是特殊的Ic型超新星，主要在晚型星系中爆炸。 它们的整体特性可能与最近观察到的一类快速演化的超新星有关，而与Ca-rich超新星类别的关系较小。