伽玛暴内激波模型中自生小尺度磁场的理论研究

In the internal shock model of gamma-ray bursts (GRBs), the prompt emission spectra are closely depended on the nature of the magnetic field in the internal shock region. The difficulties encountered by the synchrotron radiation model on the basis of large-scale uniform magnetic can be resolved by the radiation of electrons in the small-scale turbulent magnetic field. A number of studies have shown that the dimension of the small-scale magnetic fields generated by transverse plasmons is much larger than the electron skin depth. The magnetic field generated by transverse plasmons can overcome the problem that the time scale of the magnetic field induced by Weibel instability is too short due to Landau damping. Considering the collisionless nature of the high temperature relativistic plasma in the internal shock region of GRB and the mode conversion of Langmuir plasmons to transverse plasmons in the highly nonlinear system, the project aims to the investigation on the excitation of magnetic field by the interaction of transverse plasmons with relativistic electron-proton plasmas, and apply the model to explain the origin of the magnetic field in the internal shock model of GRB. The study can provide a theoretical basis for the model of prompt GRB emission based on the small-scale turbulent magnetic field.

伽玛暴内激波模型中，瞬时辐射谱与内激波处磁场的性质有着密切联系。电子在小尺度湍动磁场中的辐射可以解决大尺度均匀磁场中同步加速辐射模型解释伽玛暴瞬时辐射谱所面临的困难。研究表明，横等离激元与等离子体相互作用产生的小尺度磁场的线度远大于电子的趋肤深度。该磁场可以克服韦伯(Weibel)不稳定性产生的磁场由于朗道阻尼时标太短的问题。考虑到伽玛暴内激波处高温相对论性等离子体的无碰撞特性以及这种高度非线性系统中朗缪尔激元和横等离激元的模转换，本课题拟从动理学理论出发研究相对论电子-质子等离子体中横等离激元激发的磁场，并应用于解释伽玛暴内激波处磁场的产生。该研究可以为基于小尺度湍动磁场的伽玛暴瞬时辐射模型提供理论。

伽玛暴内激波区小尺度磁场的产生对于伽玛暴瞬时辐射谱的解释有着重要意义。韦伯(Weibel)不稳定性产生的磁场由于朗道阻尼衰减时标与观测谱的特征时标不符。考虑到火球能量的转化，伽玛暴内激波区应存在少量重子。从动理学理论出发得到了含有相对论性质子的正负电子等离子体中横等离激元激发的低频自生磁场的非线性控制方程。选取适当的伽玛暴内激波处等离子体参数，通过数值计算和模拟得到了自生磁场的性质。研究表明自生磁场的尺度远大于电子的趋肤深度能够有效地克服朗道阻尼，且磁场的强度与已有的理论估值一致。这意味着横等离激元与含有相对论性质子的正负电子等离子体相互作用可以产生长时标的小尺度磁场，从而为解释伽玛暴内激波处小尺度磁场的产生提供了一种可能的机制。