Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process
Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process
复制标题
DOI：
10.1093/mnras/stx478
复制
发表时间：
2017-01
影响因子：
4.8
通讯作者：
A. Vlasov;B. Metzger;J. Lippuner;L. Roberts;T. Thompson
中科院分区：
文献类型：
--
作者：
A. Vlasov;B. Metzger;J. Lippuner;L. Roberts;T. Thompson
我们探索来自快速旋转、强磁化的原中子星（“毫秒原磁星”）的中微子驱动风中的重元素核合成，其中磁偶极子与旋转轴对齐，并且场被假设为无静态力配置。我们使用原中子星冷却阶段风电子分数演化的当代模型，通过 r 过程核反应网络 SkyNet 处理由 Vlasov、Metzger 和 Thompson 计算的原磁星风轨迹。尽管我们没有发现任何自转周期 P 成功的第二或第三峰值 r 过程，但我们表明，P ∼ 1-5 ms 的原磁体产生的重元素丰度分布比其他等效的球形风延伸到更高的核质量数（某些元素的质量分数提高了 100-1000 倍）。最重的元素是由沿着通量管出现的流出物合成的，这些通量管掠过封闭区域并通过光柱外的赤道面附近。由于核合成模式依赖于原中子星的磁场强度和旋转速率，核心塌陷事件之间这些量的自然变化可能有助于观察到贫金属恒星中弱r过程核丰度的多样性。对于相对于旋转轴具有非零磁倾角的未对准旋转器，可以实现进一步的多样性，甚至可能包括成功的第三峰 r 过程。如果原磁体是伽玛暴的中央引擎，它们的相对论性喷流应包含特征质量数 A ≈ 100 的高质量重核，为由重核组成的超高能宇宙射线提供可能的来源，其能谱超出了质子或铁核的名义 Grezin-Zatsepin-Kuzmin 截止值。
We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, stronglymagnetized protoneutron stars (‘millisecond protomagnetars’) forwhich themagnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ∼ 1–5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of �100–1000). The heaviest elements are synthesized by outflows emerging along flux tubes that graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the protoneutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If protomagnetars are central engines for GRBs, their relativistic jets should contain a high-mass fraction of heavy nuclei of characteristic mass number ¯A ≈ 100, providing a possible source for ultrahigh energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal Grezin–Zatsepin–Kuzmin cut-off for protons or iron nuclei.