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arXiv 2410.04446astro-ph.HEphysics.plasm-ph
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结构化喷流剪切康普顿化导致GRB瞬时辐射阶段正负光谱滞后的统一理论

Unified theory of negative and positive spectral lags in GRB prompt phase due to shear Comptonization from a structured jet

Mukesh Kumar Vyas, Asaf Pe'er, Shabnam Iyyani

AI总结:

针对伽马射线暴瞬时辐射阶段的负光谱滞后及滞后转变现象,提出带速度剪切的结构化喷流模型,通过剪切康普顿化效应统一解释正负光谱滞后的成因,并将喷流洛伦兹因子范围限制在几十量级。

摘要:

在伽马射线暴(GRB)瞬时辐射阶段的光谱研究中,正光谱滞后是一种常见观测现象,表现为软光子滞后于硬光子。与该模式相反,部分GRB呈现负光谱滞后,即硬光子比软光子更晚到达。类似地,近期Fermi-LAT的观测显示,大多数GRB观测中存在高能光子晚出的现象。部分GRB还表现出从正滞后到负滞后的转变。这类负滞后及光谱滞后转变目前尚无令人信服的解释。我们证明,带有速度剪切的结构化GRB喷流可以自然产生正、负两种光谱滞后。光子通过与剪切层的反复散射获得能量,随后从更高高度逃逸,因此这些光子相比软光子存在延迟,从而产生负光谱滞后。喷流内部不存在剪切,因此会出现正滞后,这为GRB中的光谱滞后现象提供了统一图景。该理论预测,在瞬时辐射阶段的演化过程中,光谱滞后会发生从正到负的翻转。将观测到的滞后与理论预测进行比较后,将GRB喷流洛伦兹因子的可能范围限制在几十的量级。

英文摘要:

Positive spectral lags are commonly observed in gamma-ray burst (GRB) prompt phase where soft photons lag behind hard ones in their spectral studies. Opposite to this pattern, a fraction of GRBs show a negative spectral lag where hard photons arrive later compared to soft photons. Similarly, recent Fermi-LAT observations show a late onset of high-energy photons in most GRB observations. A fraction of GRBs show a transition from positive to negative lags. Such negative lags and the spectral lag transition have no convincing explanation. We show that a structured GRB jet with velocity shear naturally produces both positive and negative spectral lags. s gain energy from repeated scattering with shearing layers and subsequently escape from higher altitudes. Hence, these photons are delayed compared to soft photons producing a negative spectral lag. The inner jet has no shear and a positive lag appears providing a unified picture of spectral lags in GRBs. The theory predicts a flip in spectral lag from positive to negative within the evolution of the prompt phase. Comparison of the observed lags with the prediction of the theory limits the possible range of GRB jet Lorentz factors to be a few tens.

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