Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: IV. Thermal {\em vs.} Non-thermal Emission of the Jet Cocoon
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| Format: | Preprint |
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2026
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| _version_ | 1866918520317542400 |
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| author | Wang, Zi-Qi Huang, Xiao-Li Zhang, Hai-Ming Liang, En-Wei |
| author_facet | Wang, Zi-Qi Huang, Xiao-Li Zhang, Hai-Ming Liang, En-Wei |
| contents | A distinct thermal or quasi-thermal spectral component is occasionally observed in gamma-ray burst (GRB) prompt emission spectra. Taking GRB 090902B as a case study, we investigate its origin within a structured jet framework, in which the outflow consists of an ultra-relativistic uniform core surrounded by a structured cocoon. In the weak-scattering regime with inefficient shear acceleration, electrons pre-energized in the thin jet-cocoon interaction layer are further heated in the mixed jet-cocoon (MJC) region, forming a quasi-thermal electron distribution. Parameterizing the radial temperature profile of electrons as a power law with index $q_T$, we demonstrate that both the peak flux and spectral width of the thermal component are sensitive to maximum temperature $T_{\max}$ and $q_T$. Combined with the synchrotron emission of shock-accelerated electrons in the jet core, our model reproduces both the quasi-thermal component in the keV-MeV range and the broadband non-thermal emission observed in the time-integrated and time-resolved spectra of GRB 090902B. A comparative analysis of GRB 240825A within a shear-acceleration dominated (strong-scattering) scenario shows that shear-accelerated electrons produce broader spectra than thermalized electrons in the weak-scattering regime. These results indicate that GRB spectral diversity likely arises from the additional emission component originating in the MJC region under different physical conditions. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_25147 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: IV. Thermal {\em vs.} Non-thermal Emission of the Jet Cocoon Wang, Zi-Qi Huang, Xiao-Li Zhang, Hai-Ming Liang, En-Wei High Energy Astrophysical Phenomena A distinct thermal or quasi-thermal spectral component is occasionally observed in gamma-ray burst (GRB) prompt emission spectra. Taking GRB 090902B as a case study, we investigate its origin within a structured jet framework, in which the outflow consists of an ultra-relativistic uniform core surrounded by a structured cocoon. In the weak-scattering regime with inefficient shear acceleration, electrons pre-energized in the thin jet-cocoon interaction layer are further heated in the mixed jet-cocoon (MJC) region, forming a quasi-thermal electron distribution. Parameterizing the radial temperature profile of electrons as a power law with index $q_T$, we demonstrate that both the peak flux and spectral width of the thermal component are sensitive to maximum temperature $T_{\max}$ and $q_T$. Combined with the synchrotron emission of shock-accelerated electrons in the jet core, our model reproduces both the quasi-thermal component in the keV-MeV range and the broadband non-thermal emission observed in the time-integrated and time-resolved spectra of GRB 090902B. A comparative analysis of GRB 240825A within a shear-acceleration dominated (strong-scattering) scenario shows that shear-accelerated electrons produce broader spectra than thermalized electrons in the weak-scattering regime. These results indicate that GRB spectral diversity likely arises from the additional emission component originating in the MJC region under different physical conditions. |
| title | Shear Particle Acceleration in Structured Gamma-Ray Burst Jets: IV. Thermal {\em vs.} Non-thermal Emission of the Jet Cocoon |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2605.25147 |