论文标题
二阶费米重新计算机制和群集内桥的大规模同步无线电发射
Second order Fermi reacceleration mechanisms and large scale synchrotron radio emission in intra-cluster bridges
论文作者
论文摘要
低频阵列（Lofar）在低频下的无线电观察开始发现巨大的无线电桥，连接了一对庞大的星系簇。这些观察结果探测了原位粒子加速度的未开发机制，该机制在几个MPC $^3 $的体积上运行。数值模拟表明，这种桥梁在动态上是复杂的，并且可以在这些区域的整个体积上驱动弱的冲击和超级alfvénic湍流。在这封信中，我们首次探讨了二阶费米机制在这些特殊区域中与湍流相互作用的相对论电子的重新计算的作用。我们假设在模拟中测得的湍流通量，并采用了一种场景，在这种情况下，相对论颗粒散射的磁场线在超αNIC湍流中扩散，并且通过相同的湍流扩大了磁场。我们表明，可以在整个群集桥区域中产生陡峭的频谱和体积填充同步加速器发射，从而为无线桥提供了自然的解释。因此，无线电观察结果有可能探测比星系簇大的尺度上的能量耗散，以及在仍在探索较差的物理状态下运行的二阶费米机制。这对天体物理学和宇宙学的多个分支有潜在的影响。
Radio observations at low frequencies with the Low Frequency Array (LOFAR) start discovering gigantic radio bridges connecting pairs of massive galaxy clusters. These observations probe unexplored mechanisms of in situ particle acceleration that operate on volumes of several Mpc$^3$. Numerical simulations suggest that such bridges are dynamically complex and that weak shocks and super-Alfvénic turbulence can be driven across the entire volume of these regions. In this Letter we explore, for the first time, the role of second order Fermi mechanisms for the reacceleration of relativistic electrons interacting with turbulence in these peculiar regions. We assume the turbulent energy flux measured in simulations and adopt a scenario in which relativistic particles scatter with magnetic field lines diffusing in super-Alfvénic turbulence and magnetic fields are amplified by the same turbulence. We show that steep spectrum and volume filling synchrotron emission can be generated in the entire intra-cluster bridge region thus providing a natural explanation for radio bridges. Consequently, radio observations have the potential to probe the dissipation of energy on scales larger than galaxy clusters and second order Fermi mechanisms operating in physical regimes that are still poorly explored. This has a potential impact on several branches of astrophysics and cosmology.
