通过超新星回落中微子诊断原中子星磁场的方法

中文摘要 AI 辅助

年轻的孤立中子星表现出广泛的磁场强度范围。为了理解这种多样性的起源，在原中子星（PNS）阶段对磁场进行观测约束具有重要意义。我们提出了一种利用与超新星回落相关的中微子来诊断PNS磁场的新方法。通过对磁化PNS上的超新星回落进行一维广义相对论磁流体动力学模拟，我们研究了回落中微子的能谱如何依赖于PNS磁场强度和回落吸积率。我们发现，更强的磁场和更低的吸积率会产生更软的能谱，因为回落中微子主要是在磁层半径附近发射的，而在这些条件下磁层半径会变得更大。为了量化这种能谱软化，我们基于30 MeV以上和以下的事件率定义了一个硬度比，并引入了硬度-事件率图。利用该图，我们确定了我们的诊断方法适用的参数区域。其适用性取决于PNS磁场强度、回落吸积率、回落阶段的开始时间以及中微子质量顺序。我们还研究了其对PNS半径的依赖性，发现更大的半径会产生更软的能谱，这表明磁场与PNS致密性之间存在简并性。因此，对PNS致密性的独立约束将使我们能够更好地约束磁场。这些结果表明，未来对银河系超新星的多信使观测可以为中子星多样性提供新的窗口。

英文摘要

Young isolated neutron stars exhibit a wide range of magnetic field strengths. To understand the origin of this diversity, it is important to observationally constrain magnetic fields during the proto-neutron star (PNS) phase. We propose a novel diagnostic of PNS magnetic fields using neutrinos associated with supernova fallback. By performing one-dimensional general-relativistic magnetohydrodynamic simulations of the supernova fallback onto a magnetized PNS, we investigate how the energy spectra of the fallback neutrinos depend on the PNS magnetic field strength and the fallback accretion rate. We find that stronger magnetic fields and lower accretion rates produce softer spectra because the fallback neutrinos are emitted mainly near the magnetospheric radius, which becomes larger under these conditions. To quantify this spectral softening, we define a hardness ratio based on event rates above and below 30 MeV and introduce a hardness-event-rate diagram. Using this diagram, we identify the parameter region in which our diagnostic is applicable. Its applicability depends on the PNS magnetic field strength, fallback accretion rate, onset time of the fallback phase, and neutrino mass ordering. We also investigate the dependence on the PNS radius and find that a larger radius produces softer spectra, indicating a degeneracy between the magnetic field and PNS compactness. An independent constraint on the PNS compactness would therefore enable us to better constrain the magnetic field. These results suggest that future multimessenger observations of galactic supernovae can provide a new window into the NS diversity.

发表机构

• The University of Tokyo（东京大学）
• Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所）
• Waseda University（早稻田大学）
• Musashino Art University（武藏野美术大学）
• Tohoku University（东北大学）
• Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo（东京大学 Kavli宇宙物理数学研究所）
• Komazawa University（驹泽大学）

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备注

24 pages, 10 figures, submitted to ApJ