Adiabatic Losses and Stochastic Particle Acceleration in Gamma-Ray Burst Blast Waves
Adiabatic Losses and Stochastic Particle Acceleration in Gamma-Ray Burst Blast Waves
复制标题
伽马射线暴爆炸波中的绝热损失和随机粒子加速
DOI：
10.1086/321580
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发表时间：
2000
期刊：
影响因子：
--
通讯作者：
M. Humi
中科院分区：
文献类型：
--
作者：
C. Dermer;M. Humi
我们研究伽马射线暴（GRB）激波在扫过外部介质物质而减速过程中的绝热损失和随机粒子加速问题。假定受激流体由一个均匀膨胀的壳层来表示。非热粒子通过绝热膨胀损失的能量转化为外流的整体动能，从而能够自洽地计算激波的整体洛伦兹因子Γ的演化。结果表明，该系统的行为在相对论和非相对论极限下重现了流体动力学自相似解，并且这种形式体系适用于绝热和完全辐射两种情况之间的中间情形。通过采用基于准线性区域导出的表达式得到的能量增益率和扩散逃逸时间尺度，研究了激波中磁湍流通过随机回旋共振加速对非热粒子的激发。如果受激流体中的磁场接近其均分场值，这一过程能够将逃逸粒子加速到≳10²⁰电子伏特的能量，这与超高能宇宙射线（UHECRs）由伽马射线暴激波加速的假设相符。由于磁湍流对粒子的捕获，对于由磁流体动力学（MHD）湍流的柯尔莫哥洛夫谱加速的情况，在伽马射线暴的瞬时辐射和余辉阶段，只有能量最高的粒子能够逃逸。随着激波变为非相对论性的，并且激波费米加速变得更加重要，低能粒子开始逃逸。
We treat the problem of adiabatic losses and stochastic particle acceleration in gamma-ray burst (GRB) blast waves that decelerate by sweeping up matter from an external medium. The shocked fluid is assumed to be represented by a homogeneous expanding shell. The energy lost by nonthermal particles through adiabatic expansion is converted to the bulk kinetic energy of the outflow, permitting the evolution of the bulk Lorentz factor Γ of the blast wave to be self-consistently calculated. The behavior of the system is shown to reproduce the hydrodynamic self-similar solutions in the relativistic and nonrelativistic limits, and the formalism is applicable to scenarios that are intermediate between the adiabatic and fully radiative regimes. Nonthermal particle energization through stochastic gyroresonant acceleration with magnetic turbulence in the blast wave is treated by employing energy-gain rates and diffusive escape timescales based on expressions derived in the quasi-linear regime. If the magnetic field in the shocked fluid approaches its equipartition value, this process can accelerate escaping particles to ≳1020 eV energies, consistent with the hypothesis that ultra-high-energy cosmic rays (UHECRs) are accelerated by GRB blast waves. Because of particle trapping by the magnetic turbulence, only the highest energy particles can escape during the prompt and afterglow phases of a GRB for acceleration by a Kolmogorov spectrum of MHD turbulence. Lower energy particles begin to escape as the blast wave becomes nonrelativistic and shock Fermi acceleration becomes more important.