标题： H.E.S.S. 针对附近超新星爆发的ToO计划：在M74中的超新星候选体AT2019krl方向寻找极高能$γ$-射线辐射 显示英文标题

标题： H.E.S.S. ToO program on nearby core-collapse Supernovae: search for very-high energy $γ$-ray emission towards the SN candidate AT2019krl in M74

摘要： 虽然已知最年轻的超新星遗迹，如仙后座A，在其当前演化阶段只能将宇宙射线加速到$\sim$10$^{14}\,\mathrm{eV}$，最近的研究表明，在核心坍缩超新星的早期阶段，当高速前向激波扩展到由恒星前体风形成的致密周围介质时，粒子能量可能超过几PeV ($10^{15}\,\mathrm{eV}$)。这种环境，特别是可能表现出高达$10^{-2}M_\odot\,\mathrm{yr}^{-1}$ \cite{smith14} 的质量损失率的IIn型超新星，因此可能导致来自强子相互作用中$\pi^0$衰变的$\gamma$-射线辐射，这可能被当前的切连科夫望远镜在极高能量下探测到。这样的探测将为超新星中宇宙射线质子/核的有效加速提供直接证据，并从而对银河系宇宙射线起源这一长期存在的问题提供新的见解。 在这一背景下，高能立体望远镜系统（\hess ）自2016年以来一直在进行一项机会目标计划，以寻找此类早期极高能 $\gamma$-射线辐射，针对附近的核心坍缩超新星和超新星候选体（最多至 $\sim 10~\mathrm{Mpc}$），在发现后几周内进行观测。 在概述了这一 \hess 机会目标计划之后，我们介绍了2019年7月对暂现源 \at 的观测结果，该天体最初被分类为IIn型超新星，在星系M74中发生，距离为 $\sim 9.8\,\mathrm{Mpc}$。 尽管其性质仍不清楚，但对这一瞬变现象得出的\hess 约束被置于核心坍缩超新星预期的VHE$\gamma$射线辐射的一般背景下。 显示英文摘要

摘要： While the youngest known supernova remnants, such as Cassiopeia A, have been proven to be able to accelerate cosmic rays only up to $\sim$10$^{14}\,\mathrm{eV}$ at their present evolutionary stages, recent studies have shown that particle energies larger than a few PeV ($10^{15}\,\mathrm{eV}$) could be reached during the early stages of a core-collapse Supernova, when the high-velocity forward shock expands into the dense circumstellar medium shaped by the stellar progenitor wind. Such environments, in particular the type IIn SNe whose progenitors may exhibit mass-loss rates as high as $10^{-2}M_\odot\,\mathrm{yr}^{-1}$ \cite{smith14}, could thus lead to $\gamma$-ray emission from $\pi^0$ decay in hadronic interactions, potentially detectable with current Cherenkov telescopes at very-high energies. Such a detection would provide direct evidence for efficient acceleration of CR protons/nuclei in supernovae, and hence new insights on the long-standing issue of the origin of Galactic Cosmic Rays. In that context, the High Energy Stereoscopic System (\hess) has been carrying out a Target of Opportunity program since 2016 to search for such an early very-high-energy $\gamma$-ray emission towards nearby core-collapse supernovae and supernova candidates (up to $\sim 10~\mathrm{Mpc}$), within a few weeks after discovery. After giving an overview of this \hess\ Target of Opportunity program, we present the results obtained from the July 2019 observations towards the transient \at, originally classified as a type IIn supernova, which occurred in the galaxy M74 at $\sim 9.8\,\mathrm{Mpc}$. Although its nature still remains unclear, the derived \hess\ constraints on this transient are placed in the general context of the expected VHE $\gamma$-ray emission from core-collapse supernovae.