Thermal Components in Gamma-Ray Bursts. I. How Do They Affect Nonthermal Spectral Parameters?
Thermal Components in Gamma-Ray Bursts. I. How Do They Affect Nonthermal Spectral Parameters?
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DOI：
10.3847/1538-4365/ab42de
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发表时间：
2019-05
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影响因子：
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通讯作者：
Liang Li
中科院分区：
文献类型：
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作者：
Liang Li
伽马射线暴（GRB）瞬时发射的光谱成分主要由两个可能的来源组成：同步加速器（非热）和光球（热）。伽马射线暴的典型光谱特性可以通过主要的非热成分（类带函数或截止幂律）来建模，而其中一些具有额外的热成分（类普朗克函数）。在本文中，我们研究了热成分对非热光谱参数的影响。我们重点关注八个费米伽马射线爆发监视器爆发，其中的光谱偏离仅带函数，并且热成分很重要。我们将它们分为热主导组 I（例如 GRB 110721A）和热主导组 II（例如 GRB 090902B）。假设光谱分量完全归因于非热分量，我们发现了几个有趣的结果：（i）低能光子指数 α 变得更硬； (ii) 峰值能量Ec明显较小，并且位于黑体组件的峰值温度和截止幂律+黑体(CPL+BB)模型的峰值能量之间； (iii) 总通量F大致相同； (iv) 变化量（Δα和ΔEc）与热通量与总通量之比正相关； （v）参数关系（F-α、F-Ec 和 Ec-α）也发生了显着变化。两组中的伽玛射线暴显示出相同的结果。我们的分析表明热成分很重要，它显着影响光谱参数和相应的物理解释。
The spectral components of the prompt emission of gamma-ray bursts (GRBs) mainly consist of two possible origins: synchrotron (nonthermal) and photosphere (thermal). The typical spectral properties of GRBs can be modeled by a dominant nonthermal component (a Band-like function or cutoff power law), while some of them have an additional thermal component (a Planck-like function). In this paper, we investigate the effects of thermal components on the nonthermal spectral parameters. We focus on eight Fermi Gamma-ray Burst Monitor bursts of which the spectra deviate from a Band-only function, and the thermal components are significant. We sort them into thermal-subdominant Group I (e.g., GRB 110721A) and thermal-dominant Group II (e.g., GRB 090902B). Several interesting results are found assuming the spectral component is totally attributed to the nonthermal component: (i) the low-energy photon index α becomes harder; (ii) the peak energy Ec is significantly smaller and lies between the peak temperature of blackbody component and the peak energy of the cutoff power law + blackbody (CPL+BB) model; (iii) total flux F is generally the same; (iv) the changes (Δα and ΔEc) are positively correlated with the ratio between the thermal flux and total flux; and (v) parameter relations (F–α, F–Ec, and Ec–α) also changed prominently. The GRBs in both groups show the same results. Our analysis indicates that the thermal component is important, and it significantly affects the spectral parameters and the consequential physical interpretations.