The role of magnetic field geometry in the evolution of neutron star merger accretion discs
The role of magnetic field geometry in the evolution of neutron star merger accretion discs
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DOI：
10.1093/mnras/stz2552
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发表时间：
2019-07
影响因子：
4.8
通讯作者：
I. Christie;A. Lalakos;A. Tchekhovskoy;Rodrigo Fernández;F. Foucart;E. Quataert;D. Kasen;D. Kasen
中科院分区：
文献类型：
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作者：
I. Christie;A. Lalakos;A. Tchekhovskoy;Rodrigo Fernández;F. Foucart;E. Quataert;D. Kasen;D. Kasen
中子星星合并是吸积、抛射和r过程核合成的独特实验室。我们利用3D广义相对论磁流体动力学模拟研究了静止Kerr黑洞合并后磁几何在合并残余盘演化中的作用。我们的模拟完全捕捉质量吸积，喷射和喷流的产生，由于其异常长的持续时间超过4秒。极向合并后磁场位形产生的喷流能量Ejet =（4-30）× 1050 erg，等效能量Eiso =（4-20）× 1052 erg，张角θjet = 6-13°，持续时间tj = 1 s。伴随着喷流的产生是f_\mathrm{ej}\sim 30\！-\！的喷射。合并后椎间盘质量的40%，持续时间>1 s。我们发现，一个更自然的，纯粹的环形合并后的磁场几何形状产生大规模的极向磁通量的交替极性和条纹射流。第一个条带的E_\mathrm{jet}\simeq 2\times 10^{48}\，\mathrm{erg}$，Eiso = 1051 erg，θjet = 3.5-5°，tj = 0.1 s，随后是104 s的条带状喷流活动，f_\mathrm{ej}\simeq 27{\rm percent}}$。这种条纹的消散可以为短持续时间伽马射线暴（sGRB）的瞬发发射提供动力。我们模拟的喷流能量和持续时间跨越sGRB的范围。我们发现，尽管蓝色kilonova分量最初被红色分量隐藏在视图中，但它扩展得更快，超过了红色分量，并且对离轴观察者变得可见。与GW 170817/GRB 170817 A相比，我们的模拟相对于红色分量低估了蓝色分量的质量几倍。包括动力学喷出物和中微子吸收可能会减少这种张力。
Neutron star mergers are unique laboratories of accretion, ejection, and r-process nucleosynthesis. We used 3D general relativistic magnetohydrodynamic simulations to study the role of the post-merger magnetic geometry in the evolution of merger remnant discs around stationary Kerr black holes. Our simulations fully capture mass accretion, ejection, and jet production, owing to their exceptionally long duration exceeding 4 s. Poloidal post-merger magnetic field configurations produce jets with energies Ejet ∼ (4–30) × 1050 erg, isotropic equivalent energies Eiso ∼ (4–20) × 1052 erg, opening angles θjet ∼ 6–13°, and durations tj ≲ 1 s. Accompanying the production of jets is the ejection of $f_\mathrm{ej}\sim 30\!-\!40{{\ \rm per\ cent}}$ of the post-merger disc mass, continuing out to times >1 s. We discover that a more natural, purely toroidal post-merger magnetic field geometry generates large-scale poloidal magnetic flux of alternating polarity and striped jets. The first stripe, of $E_\mathrm{jet}\simeq 2\times 10^{48}\, \mathrm{erg}$, Eiso ∼ 1051 erg, θjet ∼ 3.5–5°, and tj ∼ 0.1 s, is followed by ≳4 s of striped jet activity with $f_\mathrm{ej}\simeq 27{{\ \rm per\ cent}}$. The dissipation of such stripes could power the short-duration gamma-ray burst (sGRB) prompt emission. Our simulated jet energies and durations span the range of sGRBs. We find that although the blue kilonova component is initially hidden from view by the red component, it expands faster, outruns the red component, and becomes visible to off-axis observers. In comparison to GW 170817/GRB 170817A, our simulations underpredict the mass of the blue relative to red component by a factor of few. Including the dynamical ejecta and neutrino absorption may reduce this tension.