论文标题
宇宙射线加速度和非热辐射在星系簇外部区域的积聚冲击处
Cosmic Ray Acceleration and Nonthermal Radiation at Accretion Shocks in the Outer Regions of Galaxy Clusters
论文作者
论文摘要
宇宙学模型预测，由于宇宙网中的细丝和空隙的超音速气体中心导致的星系簇外部区域形成了外部积聚冲击。它们的特征是高声音和alfvénic马赫数，$ m_s \ sim10-10^2 $和$ m_a \ sim10^2-10^3 $，并将其传播成$β\ equiv p_g/p_g/p_b/p_b \ gtrsim10^2 $的弱磁化等离子体。尽管预计强大的吸积冲击将是宇宙射线（CRS）的有效加速器，但尚未确认簇周围的休克加速CR的非热特征，并且这种冲击的详细加速物理学尚待理解。在这项研究中，我们首先通过二维粒子中的粒子模拟建立，即在强高$β$ shocks电子下，可以通过随机的费米加速度来预先启动，这是由于电击过渡区域中的离子 - 韦贝尔不稳定性，然后可能会注入扩散性冲击加速度。因此，我们提出，从传统的热泄漏注入中得出的模型也可以用于在吸积冲击时加速电子和离子。将这些分析模型应用于在结构形成模拟中鉴定的数值休克区，我们估计非热辐射，例如由于CR电子引起的同步辐射和逆孔子（IC）发射，以及$π^0 $ -Decay $ -Decay $γ$ - 由于CR蛋白质引起的cr蛋白质，周围是模拟的cr，围绕模拟的cr蛋白酶。我们带有注入参数的模型，$ q \ 3.5-3.8 $，预测合成同步映射，这似乎与最近对昏迷群集的无线电观察结果一致。但是，从积聚冲击中检测非热IC X射线和$γ$ - 将非常具有挑战性。我们建议，提出的分析模型可以用作宇宙减震器中CR生产的通用食谱。
Cosmology models predict that external accretion shocks form in the outer region of galaxy clusters due to supersonic gas infall from filaments and voids in the cosmic web. They are characterized by high sonic and Alfvénic Mach numbers, $M_s\sim10-10^2$ and $M_A\sim10^2-10^3$, and propagate into weakly magnetized plasmas of $β\equiv P_g/P_B\gtrsim10^2$. Although strong accretion shocks are expected to be efficient accelerators of cosmic rays (CRs), nonthermal signatures of shock-accelerated CRs around clusters have not been confirmed, and detailed acceleration physics at such shocks has yet to be understood. In this study, we first establish through two-dimensional particle-in-cell simulations that at strong high-$β$ shocks electrons can be pre-energized via stochastic Fermi acceleration owing to the ion-Weibel instability in the shock transition region, possibly followed by injection into diffusive shock acceleration. Hence, we propose that the models derived from conventional thermal leakage injection may be employed for the acceleration of electrons and ions at accretion shocks as well. Applying these analytic models to numerical shock zones identified in structure formation simulations, we estimate nonthermal radiation, such as synchrotron and inverse-Compton (IC) emission due to CR electrons, and $π^0$-decay $γ$-rays due to CR protons, around simulated clusters. Our models with the injection parameter, $Q\approx3.5-3.8$, predict synthetic synchrotron maps, which seem consistent with recent radio observations of the Coma cluster. However, the detection of nonthermal IC X-rays and $γ$-rays from accretion shocks would be quite challenging. We suggest that the proposed analytic models may be adopted as generic recipes for CR production at cosmological shocks.
