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arXiv 1901.01029astro-ph.HE
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快速射电暴中相对论激波的同步脉泽辐射:冷对等离子体的一维PIC模拟

The synchrotron maser emission from relativistic shocks in Fast Radio Bursts: 1D PIC simulations of cold pair plasmas

Illya Plotnikov, Lorenzo Sironi

摘要:

快速射电暴(FRB)的发射过程至今仍不清楚。我们研究磁星风中相对论激波的同步脉泽发射是否可以解释所观察到的FRB特性。我们进行粒子在细胞(PIC)模拟冷对等离子体中的垂直冲击,检查我们的结果之间的一致性三个PIC代码。我们确认,一个线性偏振的X-模式波是自洽产生的冲击和传播上游作为前驱波。我们发现,在磁化$σ\gtrsim 1$(即,波印廷通量与预激波流的粒子能通量的比率),激波将总入射能量的一部分$f_ξ' \approx 7 \times 10^{-4}/σ^2$转换成前驱波,如在激波系中测量的。波谱为窄带(分数宽度$\lesssim 1-3$),具有明显但不占主导地位的线状特征,因为许多共振同时起作用。在预激波(观测者)坐标系中的峰值频率是$ω^{\prime \prime}_{\rm peak} \approx 3 γ_{\rm s | u} ω_{\rm p}$,其中$γ_{\rm s|u}$是上游坐标系中的激波洛伦兹因子,$ω_{\rm p}$是等离子体频率。在$σ\gtrsim1$中,我们估计的$ω''_{\rm peak}$与以前的工作不同,激波结构呈现出由腔分离的两个孤子,峰值频率对应于腔的本征模。我们的研究结果提供了物理接地输入FRB发射模型内的磁星的情况。

英文摘要:

The emission process of Fast Radio Bursts (FRBs) remains unknown. We investigate whether the synchrotron maser emission from relativistic shocks in a magnetar wind can explain the observed FRB properties. We perform particle-in-cell (PIC) simulations of perpendicular shocks in cold pair plasmas, checking our results for consistency among three PIC codes. We confirm that a linearly polarized X-mode wave is self-consistently generated by the shock and propagates back upstream as a precursor wave. We find that at magnetizations $σ\gtrsim 1$ (i.e., ratio of Poynting flux to particle energy flux of the pre-shock flow) the shock converts a fraction $f_ξ' \approx 7 \times 10^{-4}/σ^2$ of the total incoming energy into the precursor wave, as measured in the shock frame. The wave spectrum is narrow-band (fractional width $\lesssim 1-3$), with apparent but not dominant line-like features as many resonances concurrently contribute. The peak frequency in the pre-shock (observer) frame is $ω^{\prime \prime}_{\rm peak} \approx 3 γ_{\rm s | u} ω_{\rm p}$, where $γ_{\rm s|u}$ is the shock Lorentz factor in the upstream frame and $ω_{\rm p}$ the plasma frequency. At $σ\gtrsim1$, where our estimated $ω''_{\rm peak}$ differs from previous works, the shock structure presents two solitons separated by a cavity, and the peak frequency corresponds to an eigenmode of the cavity. Our results provide physically-grounded inputs for FRB emission models within the magnetar scenario.

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