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arXiv 1602.09018astro-ph.HE
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来自宇宙伽马射线的新见解

New insights from cosmic gamma rays

Roland Diehl

摘要:

在研究核反应及其对整个宇宙的物体和现象的影响时,测量来自宇宙源的兆电子伏能量的伽马射线是核天体物理学的关键工具之一。伽马射线最直接地追踪核过程,因为它们起源于放射性衰变或高能碰撞后的核跃迁。此外,来自正电子湮灭的独特伽马射线特征落入这个天文学窗口,并在这里讨论:宇宙正电子通常是由β衰变产生的,因此也是核物理起源。产生放射性同位素的核反应发生在恒星内部和恒星爆炸,因此构成了这类研究的主要对象。近年来,热核超新星和核心坍缩超新星的放射性都被测量,并通过测量其主要能源补充了传统的超新星观测。现在正在分析大质量恒星在伽马射线中进行核合成的弥漫放射性余辉,以了解大质量恒星如何将其能量反馈并喷射到星际气体中。大型的星际空洞和超级气泡被认为是新的恒星喷出物注入的主要结构,从26 Al伽马射线光谱。最后,正电子湮灭伽马射线的令人困惑的膨胀主导强度分布被更详细地测量,但仍然没有被理解;最近的微类星体耀斑提供了证据,表明这样的物体可能是星际空间中正电子的主要来源,而不是分布式核合成。我们还简要讨论了天文学的现状和前景与望远镜的核辐射能量窗口。

英文摘要:

The measurement of gamma rays from cosmic sources at MeV energies is one of the key tools for nuclear astrophysics, in its study of nuclear reactions and their impacts on objects and phenomena throughout the universe. Gamma rays trace nuclear processes most directly, as they originate from nuclear transitions following radioactive decays or high-energy collisions with excitation of nuclei. Additionally, the unique gamma-ray signature from the annihilation of positrons falls into this astronomical window and is discussed here: Cosmic positrons are often produced from beta-decays, thus also of nuclear physics origins. The nuclear reactions leading to radioactive isotopes occur inside stars and stellar explosions, which therefore constitute the main objects of such studies. In recent years, both thermonuclear and core-collapse supernova radioactivities have been measured, and complement conventional supernova observations with measurements of their prime energy sources. The diffuse radioactive afterglow of massive-star nucleosynthesis in gamma rays is now being analysed towards how massive stars feed back their energy and ejecta into interstellar gas. Large interstellar cavities and superbubbles have been recognised to be the dominating structures where new massive-star ejecta are injected, from 26Al gamma-ray spectroscopy. Finally, the puzzling bulge-dominated intensity distribution of positron annihilation gamma rays is measured in greater detail, but still not understood; a recent microquasar flare provided evidence that such objects may be prime sources for positrons in interstellar space, rather than distributed nucleosynthesis. We also briefly discuss the status and prospects for astronomy with telescopes for the nuclear-radiation energy window.

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