THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS
THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS
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DOI：
10.1088/0004-637x/726/2/90
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发表时间：
2010-11
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影响因子：
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通讯作者：
Bing Zhang;Huirong Yan
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文献类型：
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作者：
Bing Zhang;Huirong Yan
最近对 GRB 080916C 的费米观测表明，与假定的火球相关的明亮光球层发射缺失，这表明中央发动机可能会发射坡印廷通量主导（PFD）流出。我们提出了 PFD 范围内伽马射线暴 (GRB) 瞬发发射的模型，即内部碰撞引起的磁重联和湍流 (ICMART) 模型。设想GRB中央发动机发射间歇性的、磁主导的风，并且在GRB发射区域，喷射物仍然被适度磁化（例如，1 ≲ σ ≲ 100）。与内部激波 (IS) 模型类似，迷你壳在半径 RIS ∼ Γ2cΔt 处发生内部相互作用。然而，大多数这些早期碰撞几乎没有能量耗散，但会扭曲喷射物中夹带的有序磁场线。在某一点上，磁场构型的扭曲达到允许快速重联种子发生的临界条件，从而在相互作用区域中引起相对论性 MHD 湍流。湍流进一步扭曲磁力线，从而缓解额外的磁重联，导致存储的磁场能量在跑道上释放（ICMART 事件）。粒子要么直接在重联区加速，要么在湍流区域随机加速，这些区域辐射出同步加速器光子，为观测到的伽马射线提供动力。每个ICMART事件对应GRB光变曲线中的一个宽脉冲，一个GRB由多个ICMART事件组成。该模型保留了IS和其他模型的优点，但可以克服IS模型面临的一些困难/问题（例如，效率低、冷却快、电子数过多、Amati/Yonetoku关系不一致以及缺少明亮的光球层）。在该模型中，观测到的GRB变化时间尺度可能有两个分量，一个与中央发动机时间历史相关的慢分量，另一个与发射区域中的相对论性磁湍流相关的快分量。该模型预测在瞬发GRB阶段期间每个ICMART事件（宽脉冲）中伽马射线偏振度和Ep的降低，以及中等磁化的外部反向激波。该模型可应用于具有时间分辨、无特征带函数谱的伽玛暴，例如 GRB 080916C 和费米 LAT 检测到的大多数伽玛暴。
The recent Fermi observation of GRB 080916C shows that the bright photosphere emission associated with a putative fireball is missing, which suggests that the central engine likely launches a Poynting-flux-dominated (PFD) outflow. We propose a model of gamma-ray burst (GRB) prompt emission in the PFD regime, namely, the Internal-Collision-induced MAgnetic Reconnection and Turbulence (ICMART) model. It is envisaged that the GRB central engine launches an intermittent, magnetically dominated wind, and that in the GRB emission region, the ejecta is still moderately magnetized (e.g., 1 ≲ σ ≲ 100). Similar to the internal shock (IS) model, the mini-shells interact internally at the radius RIS ∼ Γ2cΔt. Most of these early collisions, however, have little energy dissipation, but serve to distort the ordered magnetic field lines entrained in the ejecta. At a certain point, the distortion of magnetic field configuration reaches the critical condition to allow fast reconnection seeds to occur, which induce relativistic MHD turbulence in the interaction regions. The turbulence further distorts field lines easing additional magnetic reconnections, resulting in a runway release of the stored magnetic field energy (an ICMART event). Particles are accelerated either directly in the reconnection zone, or stochastically in the turbulent regions, which radiate synchrotron photons that power the observed gamma rays. Each ICMART event corresponds to a broad pulse in the GRB light curve, and a GRB is composed of multiple ICMART events. This model retains the merits of IS and other models, but may overcome several difficulties/issues faced by the IS model (e.g., low efficiency, fast cooling, electron number excess, Amati/Yonetoku relation inconsistency, and missing bright photosphere). Within this model, the observed GRB variability timescales could have two components, one slow component associated with the central engine time history, and another fast component associated with relativistic magnetic turbulence in the emission region. The model predicts a decrease of gamma-ray polarization degree and Ep in each ICMART event (broad pulse) during the prompt GRB phase, as well as a moderately magnetized external reverse shock. The model may be applied to the GRBs that have time-resolved, featureless Band-function spectra, such as GRB 080916C and most GRBs detected by Fermi LAT.