Does Prompt Gamma-Ray Burst Fireball Composition Impact on Afterglow Emission? Case Study for Long GRBs 080916C/090902B and Short GRBs 090510/130603B
伽马射线暴瞬时火球成分是否影响余辉发射?基于长暴080916C/090902B和短暴090510/130603B的案例研究
Broadband observations with the Fermi mission reveal that a large fraction of gamma-ray burst (GRB) spectra are dominated by nonthermal emission, while a small fraction are dominated by thermal/quasi-thermal emission, likely indicating the difference in jet composition among GRBs. By selecting two typical long GRBs (080916C and 090902B) and two short GRBs (130603B and 090510), we present a comparative analysis to investigate whether the composition of prompt GRB jets influences the afterglow emission for bursts originating from both massive star collapse and compact binary mergers. Incorporating emission from both primary and cascade electron populations, we fit the multiwavelength afterglow lightcurves of these GRBs with the standard forward shock model and analyze the particle acceleration and radiation physics of the jets. Our results show that the afterglow lightcurve evolution with the characteristic parameters is not related to the composition of the GRB fireball but rather depends on the ambient medium density. The early UV-optical afterglows of the two long GRBs are dominated by synchrotron emission from cascaded e<SUP>±</SUP> pairs produced via the γγ annihilation process, whereas this is not the case for the two short GRBs. These results suggest that the internal energy of the fireball is converted into jet kinetic energy during the prompt phase, and that the fireball composition leaves no detectable footprint on the afterglow jet. Instead, the density of the ambient medium plays an essential role in shaping the afterglow emission.
展开 ▾首次系统比较Poynting通量主导与物质主导喷流的余辉,并纳入级联辐射过程,揭示长暴早期光学余辉由级联同步辐射主导。
GRB喷流成分是长期未解之谜。既往观测显示GRB 090902B瞬时辐射以准热成分为主,支持物质火球模型 Toma+ 2011 Zhang+ 2011,而GRB 080916C无热成分,指示磁化喷流 Zhang+ 2009。本研究基于外激波模型,对两类长暴和短暴进行余辉拟合,并系统纳入级联辐射 Huang+ 2021,发现火球成分对余辉无影响,环境密度起决定作用;长暴早期光学余辉由级联同步辐射主导。未来需扩大样本并探究磁能-动能转换效率,以建立统一物理图像。
预印本 2026-06-20 · 接收 2026-06-19 · 刊出 2026-07-10 · 收录 2026-07-22