A Comprehensive Consistency Check between Synchrotron radiation and the Observed Gamma-ray Burst Spectra

TL;DR

This study performs a detailed time-resolved spectral analysis of 53 bright gamma-ray bursts observed by Fermi/GBM, testing synchrotron radiation models against empirical fits and finding that synchrotron, especially single power-law, can successfully explain most spectra.

Contribution

It provides a comprehensive comparison of synchrotron models with empirical fits for GRB spectra, demonstrating the viability of synchrotron radiation as the prompt emission mechanism.

Findings

Synchrotron models, except fast cooling, fit most spectra well.

Single power-law synchrotron model is most preferred.

Electron distribution indices show flux-tracking behavior.

Abstract

We performed a time-resolved spectral analysis of 53 bright gamma-ray bursts (GRBs) observed by \textit{Fermi}/GBM. Our sample consists of 908 individual spectra extracted from the finest time slices in each GRB. We fitted them with the synchrotron radiation model by considering the electron distributions in five different cases: mono-energetic, single power-law, Maxwellian, traditional fast cooling, and broken power-law. Our results were further qualified through Bayesian Information Criterion (BIC) by comparing with the fit by empirical models, namely the so-called Band function and cut-off power-law models. Our study showed that the synchrotron models, except for the fast-cooling case, can successfully fit most observed spectra, with the single power-law case being the most preferred. We also found that the electron distribution indices for the single power-law synchrotron fit in more than half of our spectra exhibits flux-tracking behavior, i.e., the index increases/decreases with the flux increasing/decreasing, implying that the distribution of the radiating electrons is increasingly narrower with time before the flux peaks and becomes more spreading afterward. Our results indicate that the synchrotron radiation is still feasible as a radiation mechanism of the GRB prompt emission phase.