相对论性MHD波中的辐射过程：圆偏振Alfvén波情形
Radiation Process in Relativistic MHD Waves: the Case of Circularly Polarized Alfvén Wave
AI总结：
本文研究相对论性圆偏振Alfvén波中电子的辐射机制，揭示电场对低能和高能电子发射率的不同影响，并解释GRB谱中的GeV额外成分。
摘要：
高磁化等离子体中的湍流可以是相对论性的，并感应出与背景磁场相当的电场。如此强的电场会影响非热电子的发射过程。作为阐明相对论性湍流中发射过程的第一步，我们研究了相对论性圆偏振Alfvén波中电子的辐射过程。尽管感应电场会提升Larmor半径小于波长的低能电子的平均能量，但由于回旋运动轨迹被拉长，这类电子的发射率受到抑制。高能电子的轨迹会被小尺度电场扰动，从而增强发射率。由于在圆偏振Alfvén波中，E×B漂移的有效Lorentz因子约为√2，其与标准同步辐射的偏离并不十分显著。然而，波中的幂律能量注入可产生凹形光子谱，这类似于GRB谱中观测到的GeV额外成分。如果湍流电场是GRB中GeV额外成分的成因，那么对典型电子能量和磁场的估计就应大幅修正。
英文摘要：
Turbulence in highly magnetized plasma can be relativistic and induce an electric field comparable to the background magnetic field. Such a strong electric field can affect the emission process of non-thermal electrons. As the first step toward elucidating the emission process in relativistic turbulence, we study the radiation process of electrons in relativistic circularly polarized Alfvén waves. While the induced electric field boosts the average energy of low-energy electrons with a Larmor radius smaller than the wavelength, the emissivity for such electrons is suppressed because of the elongated gyro-motion trajectory. The trajectory of high-energy electrons is shaken by the small-scale electric field, which enhances the emissivity. Since the effective Lorentz factor of $E\times B$ drift is $\simeq\sqrt{2}$ in the circularly polarized Alfvén waves, the deviation from the standard synchrotron emission is not so prominent. However, a power-law energy injection in the waves can produce a concave photon spectrum, which is similar to the GeV extra component seen in GRB spectra. If the turbulence electric field is responsible for the GeV extra component in GRBs, the estimates of the typical electron energy and magnetic field should be largely altered.
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