Helium as an Indicator of the Neutron-Star Merger Remnant Lifetime and its Potential for Equation of State Constraints
Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯·玻尔研究所）；Cosmic Dawn Center（宇宙黎明中心）；GSI Helmholtzzentrum für Schwerionenforschung（吉森亥姆霍兹重离子研究中心）；Astrophysical Big Bang Laboratory, RIKEN Cluster for Pioneering Research（理研前沿研究集群天体物理大爆炸实验室）；Helmholtz Forschungsakademie Hessen für FAIR (HFHF)（黑森亥姆霍兹FAIR研究学院）；School of Physics, Trinity College Dublin（都柏林圣三一学院物理系）；Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast（贝尔法斯特女王大学数学与物理学院天体物理研究中心）
Albert Sneppen, Oliver Just, Andreas Bauswein, Rasmus Damgaard, Darach Watson, Luke J. Shingles, Christine E. Collins, Stuart A. Sim, Zewei Xiong, Gabriel Marti… 展开作者
Albert Sneppen, Oliver Just, Andreas Bauswein, Rasmus Damgaard, Darach Watson, Luke J. Shingles, Christine E. Collins, Stuart A. Sim, Zewei Xiong, Gabriel Martinez-Pinedo, Theodoros Soultanis, Vimal Vijayan
The time until black hole formation in a binary neutron-star (NS) merger contains invaluable information about the nuclear equation of state (EoS) but has thus far been difficult to measure. We propose a new way to constrain the merger remnant's NS lifetime, which is based on the tendency of the NS remnant neutrino-driven winds to enrich the ejected material with helium. Based on the He I $λ1083.3$ nm line, we show that the feature around 800-1200 nm in AT2017gfo at 4.4 days seems inconsistent with a helium mass fraction of $X_{\mathrm{He}} \gtrsim 0.05$ in the polar ejecta. Our recent neutrino-hydrodynamic simulations of merger remnants are only compatible with this limit if the NS remnant collapses within 20-30 ms. Such a short lifetime implies that the total binary mass of GW170817, $M_\mathrm{\rm tot}$, lay close to the threshold binary mass for direct gravitational collapse, $M_\mathrm{thres}$, for which we estimate $M_{\mathrm{thres}}\lesssim 2.93 M_\odot$. This upper bound on $M_\mathrm{thres}$ yields upper limits on the radii and maximum mass of cold, non-rotating NSs, which rule out simultaneously large values for both quantities. In combination with causality arguments, this result implies a maximum NS mass of $M_\mathrm{max}\lesssim2.3 M_\odot$. The combination of all limits constrains the radii of 1.6 M$_\odot$ NSs to about 12$\pm$1 km for $M_\mathrm{max}$ = 2.0 M$_\odot$ and 11.5$\pm$1 km for $M_\mathrm{max}$ = 2.15 M$_\odot$. This $\sim2$ km allowable range then tightens significantly for $M_\mathrm{max}$ above $\approx2.15$ M$_\odot$. This rules out a significant number of current EoS models. The short NS lifetime also implies that a black-hole torus, not a highly magnetized NS, was the central engine powering the relativistic jet of GRB170817A. Our work motivates future developments... [abridged]
Helium emission from Balmer-dominated shocks in Type Ia supernova remnants provides constraints to their progenitor systems
The University of New South Wales（新南威尔士大学）；Australian National University（澳大利亚国立大学）；Towson University（陶森大学）；Naval Research Laboratory（海军研究实验室）；Trinity College Dublin, The University of Dublin（都柏林三一学院，都柏林大学）
Deciphering the explosion mechanism of Type Ia SNe using their remnants II: a deep dive into double detonations with SNR 0509-67.5
University of Virginia（弗吉尼亚大学）；Virginia Institute for Theoretical Astronomy, University of Virginia（弗吉尼亚大学理论天体物理研究所）；Towson University（陶森大学）；The University of New South Wales（新南威尔士大学）；Australian National University（澳大利亚国立大学）；South African Astronomical Observatory（南非天文台）；University of Cape Town（开普敦大学）；National Institute for Theoretical and Computational Sciences（国家理论与计算科学研究所）
A hybrid type Ia supernova with an early flash triggered by helium-shell detonation
Ia型超新星（SNe Ia）是由碳氧白矮星的热核爆炸产生的。虽然它们光变曲线的均匀性使它们成为强大的宇宙学距离指标，但关于它们的祖先和爆炸机制的长期问题仍然存在。最近探测到的一个特殊的亚发光Ia超新星的早期紫外脉冲已被声称是通过单简并通道的同伴-喷出物相互作用的新证据。在这里，我们报告了一个Ia型超新星爆炸后0.5天在$\sim$发现了一个显著的红色闪光，它显示了不同Ia型超新星子类的混合特征：一个典型的正常亮度Ia型超新星的光变曲线，但具有强烈的钛反射，通常在亚发光的光谱中看到。我们认为，这种混合型超新星Ia的早期闪光与先前提出的同伴-喷出物相互作用等情景的预测不同。相反，它可以自然地解释为SN爆炸，由一个薄氦壳爆炸引发，该薄氦壳发生在一颗近千倍塞卡质量的白矮星（$\gtrsim$ 1.3 M $_{\odot}$）和一颗低当量的$^{56}$ Ni上，或者发生在一颗亚千倍塞卡质量的白矮星（$\sim$ 1.0 M $_{\odot}$）和一颗质量较小的白矮星合并上。这一发现提供了令人信服的证据，证明以前提出的爆炸模型的一个分支，氦点火情景，在自然界中确实存在，这样的情景可能解释白矮星在更大质量范围内的爆炸，而不是以前的假设。
Hydrodynamical simulations of helium-ignited binary white dwarf mergers
University of Massachusetts Dartmouth（麻省大学达特茅斯分校）；Center for Scientific Computing and Data Science Research University of Massachusetts, Dartmouth（麻省大学达特茅斯分校科学计算与数据科学研究中心）；Georgia Institute of Technology（佐治亚理工学院）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）
