GRB 250920C 中热与非热辐射成分的演化
The Evolution of Thermal and Non-thermal Emission Components in GRB 250920C
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中文总结 AI 辅助
通过Fermi/GBM和Swift/BAT数据的时间分辨光谱分析，发现GRB 250920C的EI阶段由热辐射主导，而EII阶段由非热同步辐射主导，表明喷流从火球主导向坡印廷通量主导转变。
中文摘要 AI 辅助
我们利用费米伽马射线暴监测仪（Fermi/GBM）和雨燕卫星爆发警报望远镜（Swift/BAT）的数据，对GRB 250920C进行了时间分辨的光谱分析。瞬时辐射由两个明显不同的阶段（EI和EII）组成，二者被一个显著的宁静间隔隔开。我们采用经验模型、热模型、复合模型以及物理同步辐射模型进行了贝叶斯光谱拟合。在EI阶段，光谱显示出额外热成分的清晰证据。在大多数亮时间bin中，黑体+幂律（BB+PL）模型更受青睐，联合Fermi/GBM和Swift/BAT的拟合进一步支持该成分的存在。黑体温度总体上随时间降低，黑体通量遵循脉冲轮廓，热通量占比保持较高。火球参数估计给出光球层洛伦兹因子为数百，初始半径$r_{0}\sim10^{9}$--$10^{10}$厘米，$1+\sigma_{0}$量级为1，且$\eta\gg1$，支持热主导的重子喷流。相比之下，EII阶段以非热辐射为主。其低能光子谱指数未显著超过同步辐射死亡线，光谱可由衰减磁场中的快速冷却同步辐射很好地描述。磁化约束给出$\sigma_{\min}\sim1.1$--$4.3$。由于这些值超过1，表明EII阶段可能由坡印廷通量主导。因此，这些结果提示GRB 250920C可能从火球主导的EI阶段向坡印廷通量主导的EII阶段发生转变。
英文摘要
We present a temporal and time-resolved spectral analysis of GRB 250920C using \textit{Fermi}/GBM and \textit{Swift}/BAT data. The prompt emission consists of two distinct episodes, EI and EII, separated by a significant quiescent interval. We perform Bayesian spectral fitting with empirical, thermal, composite, and physical synchrotron models. In EI, the spectra show clear evidence for an additional thermal component. The BB+PL model is preferred in most bright time bins, and joint \textit{Fermi}/GBM+\textit{Swift}/BAT fits further support the presence of this component. The blackbody temperature generally decreases with time, the blackbody flux follows the pulse profile, and the thermal flux fraction remains high. Fireball-parameter estimates give a photospheric Lorentz factor of a few hundred and an initial radius of $r_{0}\sim10^{9}$--$10^{10}$ cm, with $1+σ_{0}$ of order unity and $η\gg1$, supporting a thermally dominated baryonic outflow. In contrast, EII is dominated by non-thermal emission. Its low-energy photon indices do not significantly exceed the synchrotron line of death, and the spectra are well described by fast-cooling synchrotron radiation in a decaying magnetic field. The magnetization constraint gives $σ_{\min}\sim1.1$--$4.3$. Since these values exceed unity, they suggest that EII may be Poynting-flux dominated. These results therefore suggest a possible transition in GRB 250920C from a fireball-dominated EI phase to a Poynting-flux-dominated EII phase.
发表机构
- Yunnan University（云南大学）
- Yunnan Normal University（云南师范大学）
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