http://arxiv.org/abs/1905.02340
The spectral components of prompt emission of gamma-ray bursts (GRBs) mainly consist of two possible origins: synchrotron (non-thermal) and photosphere (thermal). The typically spectral properties of GRBs can be modeled by a dominant non-thermal component (Band-like function or cutoff power-law), some of them have an additional thermal component (Planck-like function). In this paper, in order to study how the thermal components affect the non-thermal spectral parameters, we focus on eight {\it Fermi}-GBM bursts of which the spectra deviate from a Band-only function, and the thermal components are significant. We sort them into thermal-sub-dominant Group I (e.g. 110721A) and thermal-dominant Group II (e.g., 090902B). Several interesting results are found if assuming the spectrum is totally non-thermal, ignoring the contribution from the thermal blackbody component: (i) the low-energy photon index $\alpha$ becomes harder; (ii) the peak energy $E_{\rm c}$, is significantly smaller, and lies between the peak temperature of blackbody component and the peak energy of CPL+BB model; (iii) total flux $F$, is generally the same; (iv) the changes ($\Delta \alpha$ and $\Delta E_{\rm c}$) are positively correlated with the ratio between the thermal flux and total flux; (v) parameter relations ($F-\alpha$, $F-E_{\rm c}$ and $E_{\rm c}$-$\alpha$) are also changed prominently. Two group samples share the same results. Our analysis indicates that the thermal component shall be cautiously valued, it markedly affects the spectral parameters, and the consequent physical interpretations.
L. Li
Wed, 8 May 19
9/48
Comments: 32 pages, 62 figures, 9 tables. Comments welcome
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