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arXiv 1907.04863astro-ph.HEgr-qc
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通过核塌缩超新星中的非对称中微子发射对原中子星早期可能的线性加速

Possible early linear acceleration of proto-neutron stars via asymmetric neutrino emission in core-collapse supernovae

Hiroki Nagakura, Kohsuke Sumiyoshi, Shoichi Yamada

摘要:

在这封{ \it Letter}中,我们给出了一个轴对称CCSN模拟的结果,该模拟对中微子输运和原中子星(PNS)的自行进行了适当的处理,其中在反弹后的$300$ ms时间内观察到与非对称中微子发射相关的显著的PNS加速。我们发现,这些不对称的中微子发射在这一阶段的PNS加速中起着重要的作用。PNS自行与不对称喷出物之间的相关性类似于流体动力学起源的中子星(NS)反冲。电子型中微子($ν_{\rm e}$)和它们的反粒子($\barν_{\rm e}$)在南北半球之间都具有$\sim 10\%$水平的不对称性,而其他重轻子中微子($ν_x$)的$\sim 1 \%$不对称性要小得多。$\barν_{\rm e}$和$ν_x$的发射在激波膨胀较强的半球较高,而$ν_{\rm e}$的发射在相对的半球增强:总的来说,中微子携带一些线性动量到激波膨胀较强的半球。这种不对称性归因于电子分数($Y_e$)在PNS包层中的非球形分布。虽然它类似于LESA(轻子发射自维持不对称),但$Y_e$不对称似乎与PNS运动有关:后者通过破坏PNS包层中物质分布的对称性来触发PNS包层中的横向圆周运动,然后通过对流、横向中微子扩散和物质压力梯度的组合来维持。我们的研究结果可能会对目前的理论NS踢机制的影响,虽然需要长期的模拟,以评估其对后来的演变的影响。

英文摘要:

In this {\it Letter}, we present the result of an axisymmetric CCSN simulation conducted with appropriate treatments of neutrino transport and proper motions of proto-neutron star (PNS), in which a remarkable PNS acceleration is observed in association with asymmetric neutrino emissions by the time of $300$ms after bounce. We find that these asymmetric neutrino emissions play important roles in the acceleration of PNS in this phase. The correlation between the PNS proper motion and the asymmetric ejecta is similar to that in the neutron star (NS) kick of hydrodynamic origin. Both electron-type neutrinos ($ν_{\rm e}$) and their anti-particles ($\barν_{\rm e}$) have $\sim 10\%$ level of asymmetry between the northern and southern hemispheres, while other heavy-leptonic neutrinos ($ν_x$) have much smaller asymmetry of $\sim 1 \%$. The emissions of $\barν_{\rm e}$ and $ν_x$ are higher in the hemisphere of stronger shock expansion whereas the $ν_{\rm e}$ emission is enhanced in the opposite hemisphere: in total the neutrinos carry some linear momentum to the hemisphere of the stronger shock expansion. The asymmetry is attributed to the non-spherical distribution of electron-fraction ($Y_e$) in the envelope of PNS. Although it is similar to LESA (lepton-emission self-sustained asymmetry), the $Y_e$ asymmetry seems to be associated with the PNS motion: the latter triggers lateral circular motions in the envelope of PNS by breaking symmetry of the matter distribution there, which are then sustained by a combination of convection, lateral neutrino diffusion and matter-pressure gradient. Our findings may have an influence on the current theories on the NS kick mechanism although long-term simulations are required to assess their impact on the later evolution.

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