Numerical GR MHD simulations of the post-merger system with a composition-dependent equation of state
Agnieszka Janiuk, Gerardo Urrutia
备注：
6 pages, 5 figures. Accepted for publication in conference proceeding.The European Physical Society Conference on High Energy Physics (EPS-HEP2023), held in Hamburg, on August 21-25, 2023
借助我们用于守恒相对论磁流体力学的代码 HARM_COOL_EOS，我们开发了一种新方案，用于模拟致密双星并合后形成的系统。我们的代码使用稠密物质的表格状态方程，考虑中微子泄漏，并通过示踪粒子方法追踪质量外流。我们讨论了数值方案，并介绍了代码中包含的恢复方法。我们还展示了一项数值模拟结果，该模拟针对双中子星或中子星与恒星级质量黑洞并合后的并合后系统。等离子体高度富中子，因此抛射物质中的 r 过程核合成可能导致不稳定重同位素的产生。它们负责产生被观测为千新星的电磁信号。此外，磁化的中微子驱动风可以作为相对论性喷流的准直机制。
英文摘要：
By means of HARM\_COOL\_EOS, which is our code for conservative relativistic magnetohydrodynamics, we developed a new scheme for the simulation of a system formed after compact binary merger. Our code works with a tabulated equation of state of dense matter, accounts for the neutrino leakage, and follows the mass outflows via the tracer particle method. We discuss the numerical scheme, and present the recovery method included in our code. We also show results of a numerical simulation, addressed to the post-merger system after the coalescence of binary neutron stars, or a neutron star with a stellar mass black hole. The plasma is very neutron-rich, so the r-process nucleosynthesis in the ejected material may lead to unstable heavy isotopes creation. They are responsible for an electromagnetic signal, observed as a kilonova. In addition, the magnetized, neutrino-driven wind can act as a collimating mechanism for the relativistic jet.
Remnant accretion disks formed in compact object mergers are an important ingredient in the understanding of electromagnetic afterglows of multi-messenger gravitational-wave events. Due to magnetically and neutrino driven winds, a significant fraction of the disk mass will eventually become unbound and undergo r-process nucleosynthesis. While this process has been studied in some detail, previous studies have typically used approximate initial conditions for the accretion disks, or started from purely hydrodynamical simulations. In this work, we analyse the properties of accretion disks formed…
We examine the long-term evolution of accretion tori around black hole (BH) remnants of compact object mergers involving at least one neutron star, to better understand their contribution to kilonovae and the synthesis of r-process elements. To this end, we modify the unsplit magnetohydrodynamic (MHD) solver in FLASH4.5 to work in non-uniform three-dimensional spherical coordinates, enabling more efficient coverage of a large dynamic range in length scales while exploiting symmetries in the system. This modified code is used to perform BH accretion disk simulations that vary the initial magnet…
Long-term ideal and resistive magnetohydrodynamics (MHD) simulations in full general relativity are performed for a massive neutron star formed as a remnant of binary neutron star mergers. Neutrino radiation transport effects are taken into account as in our previous papers. The simulation is performed in axial symmetry and without considering dynamo effects as a first step. In the ideal MHD, the differential rotation of the remnant neutron star amplifies the magnetic-field strength by the winding in the presence of a seed poloidal field until the electromagnetic energy reaches $\sim 10\%$ of …
Inverse Transfer in Non-helical 2D Collisionless Magnetic Turbulence: Island-Merger Picture with Kinetic Effects
Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大李政道研究所）；School of Mathematics, Physics and Statistics, Shanghai Polytechnic University（上海理工大学数学与统计学院）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Key Laboratory for Particle Physics, Astrophysics and Cosmology (MOE), Shanghai Key Laboratory for Particle Physics and Cosmology, Shanghai Jiao Tong University（上海交通大学粒子物理、天体物理与宇宙学教育部重点实验室）
Rose-Hulman Institute of Technology（罗斯-赫尔曼理工学院）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；Institute of Astronomy, Russian Academy of Sciences（俄罗斯科学院天文研究所）；Purdue University（普渡大学）
Magnetic fields are expected to play a key role in the dynamics and the ejection mechanisms that accompany the merger of two neutron stars. General relativistic magnetohydrodynamic (MHD) simulations offer a unique opportunity to unravel the details of the ongoing physical processes. Nevertheless, current numerical studies are severely limited by the fact that any affordable resolution remains insufficient to fully capture the small-scale dynamo, initially triggered by the Kelvin-Helmholtz instability, and later sourced by several MHD processes involving differential rotation. Here, we alleviat…
Simulating the quasi-ballistic regime of a short Gamma-Ray Burst jet
SISSA（的里雅斯特国际高等研究学院）；INAF, Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；INFN, Sezione di Trieste（意大利国家核物理研究院的里雅斯特分部）；INFN, Sezione di Padova（意大利国家核物理研究院帕多瓦分部）；INAF, Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）
Finite-temperature equation of state (EoS) and the composition of dense nuclear and hypernuclear matter under conditions characteristic of neutron star binary merger remnants and supernovas are discussed. We consider both neutrino free-streaming and trapped regimes which are separated by a temperature of a few MeV. The formalism is based on covariant density functional (CDF) theory for the full baryon octet with density-dependent couplings, suitably adjusted in the hypernuclear sector. The softening of the EoS with the introduction of the hyperons is quantified under various conditions of lept…
Magnetohydrodynamic (MHD) turbulence in neutron star (NS) merger remnants can impact their evolution and multimessenger signatures, complicating the interpretation of present and future observations. Due to the high Reynolds numbers and the large computational costs of numerical relativity simulations, resolving all the relevant scales of the turbulence will be impossible for the foreseeable future. Here, we adopt a method to include subgrid-scale turbulence in moderate resolution simulations by extending the large-eddy simulation (LES) method to general relativity (GR). We calibrate our subgr…
Neutron star mergers are very violent events involving extreme physical processes: dynamic, strong-field gravity, large magnetic field, very hot, dense matter, and the copious production of neutrinos. Accurate modeling of such a system and its associated multi-messenger signals, such as gravitational waves, short gamma ray burst, and kilonova, requires the inclusion of all these processes, and is increasingly important in light of advancements in multi-messenger astronomy generally, and in gravitational wave astronomy in particular (such as the development of third-generation detectors). Sever…
We present a systematic numerical relativity study of the impact of different treatment of microphysics and grid resolution in binary neutron star mergers. We consider series of simulations at multiple resolutions comparing hydrodynamics, neutrino leakage scheme, leakage augmented with the M0 scheme and the more consistent M1 transport scheme. Additionally, we consider the impact of a sub-grid scheme for turbulent viscosity. We find that viscosity helps to stabilise the remnant against gravitational collapse but grid resolution has a larger impact than microphysics on the remnant's stability. …
Parametric equations of state (EoSs) provide an important tool for systematically studying EoS effects in neutron star merger simulations. In this work, we perform a numerical validation of the M*-framework for parametrically calculating finite-temperature EoS tables. The framework, introduced in Raithel et al. (2019), provides a model for generically extending any cold, beta-equilibrium EoS to finite-temperatures and arbitrary electron fractions. In this work, we perform numerical evolutions of a binary neutron star merger with the SFHo finite-temperature EoS, as well as with the M*-approxima…
The first binary neutron star merger has already been detected in gravitational waves. The signal was accompanied by an electromagnetic counterpart including a kilonova component powered by the decay of radioactive nuclei, as well as a short $γ$-ray burst. In order to understand the radioactively-powered signal, it is necessary to simulate the outflows and their nucleosynthesis from the post-merger disk. Simulating the disk and predicting the composition of the outflows requires general relativistic magnetohydrodynamical (GRMHD) simulations that include a realistic, finite-temperature equation…
A Magnetic Unification of Merging Supermassive Black Hole Binaries
Institute of Science and Technology Austria (ISTA)（奥地利科学技术研究所）；Department of Astronomy, Columbia University（哥伦比亚大学天文学系）；Department of Physics, Columbia University（哥伦比亚大学物理系）
The kilonova (KN) associated with the binary neutron star (BNS) merger GW170817 is the only known electromagnetic counterpart to a gravitational wave source. Here we produce a sequence of radiative transfer models (using $\textsc{tardis}$) with updated atomic data, and compare them to accurately calibrated spectra. We use element compositions from nuclear network calculations based on a realistic hydrodynamical simulation of a BNS merger. We show that the blue spectrum at +1.4 days after merger requires a nucleosynthetic trajectory with a high electron fraction. Our best-fitting model is compo…
Impact of in situ nuclear networks and atomic opacities on neutron star merger ejecta dynamics, nucleosynthesis, and kilonovae
Friedrich-Schiller-Universität Jena（耶拿弗里德里希·席勒大学）；Università di Trento（特伦托大学）；INFN-TIFPA, Trento Institute for Fundamental Physics and Applications（意大利国家核物理研究所-特伦托基础物理与应用研究所）；Los Alamos National Laboratory（洛斯阿拉莫斯国家实验室）
Reverse Shock Emission Driven By Post-Merger Millisecond Magnetar Winds: Effects of the Magnetization Parameter
对短持续时间伽马射线暴的研究提供了越来越多的证据，证明很大一部分双中子星合并导致了稳定的毫秒磁星的形成。毫秒磁星发射的坡印廷通量可以留下独特的电磁特征，揭示磁星风中的能量耗散过程。在以前的研究中（Wang & Dai 2013 b; Wang et al. 2015），我们假设磁星风完全由轻子主导，因此磁星风中的电子/正电子被扩散激波加速。然而，对脉冲星风星云的理论模拟表明，在许多情况下，脉冲星风中的磁场能量可能足够强，足以抑制扩散激波加速。本文研究了磁星风在任意磁化参数$σ$下的反向激波发射和正向激波发射。我们发现，反向冲击辐射强烈地依赖于$σ$，特别是，$σ\sim 0.3$导致最强的反向冲击辐射。未来的观测将有助于诊断磁星风的组成。
