A Comprehensive Analysis of Fermi Gamma-Ray Burst Data with Thermal and Non-thermal Component
Chen Wang
College of Physics and Electronics information, Yunnan Normal University, Kunming 650500, China.
Zhao-Yang Peng *
College of Physics and Electronics information, Yunnan Normal University, Kunming 650500, China.
Shun Huang
College of Physics and Electronics information, Yunnan Normal University, Kunming 650500, China.
*Author to whom correspondence should be addressed.
Abstract
Aims: We have investigated the properties of thermal and non-thermal components as well as the effect of the thermal components on the overall gamma-ray burst (GRB) spectra with 20 GRBs observed by Fermi/GBM.
Methodology: We first comprehensively compare the fitting results of the two different models (Band Only and Band+Blackbody (BB)) in the time-resolved spectra. We then use a power-law with an exponential cutoff + Blackbody+ power law (CPL+BB+PL) model to fit the time-resolved spectra. Finally, we present the spectral evolutions between the spectral parameters and their physical significance.
Results: The thermal component decreases the low-energy index α and does not seem to affect high-energy index β; the thermal component makes the peak energy Ep increase and it leads to faster decay of Ep in decaying episodes. Four GRBs can be fitted by CPL+BB+PL model, which shows that PL component appears in the energy spectrum at the beginning of the fireball explosion.
Conclusion: (i) The radiation mechanisms of a few bursts are consistent with the synchrotron radiation while three bursts can be explained by jitter radiation; (ii) comparing the particle acceleration models in GRBs, the magnetic reconnection is more suitable to the prompt emission than the internal shock; (iii) the correlation between spectral peak energy Ep and thermal temperature kT shows that there are magnetically-dominant jets in the GRBs; (IV) the Ep−Fp (energy flux) relation is weaker in Band+BB, which may be regarded as one of the evidences of the existence of the thermal radiation in GRB prompt emission.
Keywords: Gamma-ray bursts, general, methods, statistical, radiation mechanisms, thermal components non-thermal components
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References
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