Spectral Diversities of Gamma-ray Bursts in High Energy Bands: Hints from Turbulent Cascade

TL;DR

This paper investigates gamma-ray burst spectral diversities using turbulent cascade models, classifying GRBs based on spectral shapes and explaining these variations through turbulence spectral indices and reconnection processes.

Contribution

It introduces a turbulence-based model to explain high-energy spectral diversities in GRBs, linking spectral shapes to turbulent cascade mechanisms and reconnection processes.

Findings

N-GRBs are consistent with a Kolmogorov turbulence index of 7/3.

S-GRB spectra are explained by kinetic magnetic reconnection turbulence.

H-GRB spectra are associated with inverse turbulent cascade during large-scale reconnection.

Abstract

We statistically examine the gamma-ray burst (GRB) photon indices obtained by the Fermi-GBM and Fermi-LAT observations and compare the LAT GRB photon indices to the GBM GRB photon indices. We apply the jitter radiation to explain the GRB spectral diversities in the high-energy bands. In our model, the jitter radiative spectral index is determined by the spectral index of the turbulence. We classify GRBs into three classes depending on the shape of the GRB high-energy spectrum when we compare the GBM and LAT detections: the GRB spectrum is concave (GRBs turn out to be softer and are labeled as S-GRBs), the GRB spectrum is convex (GRBs turn out to be harder and are labeled as H-GRBs), and the GRBs have no strong spectral changes (labeled as N-GRBs). A universal Kolmogorov index 7/3 in the turbulent cascade is consistent with the photon index of the N-GRBs. The S-GRB spectra can be explained by the turbulent cascade due to the kinetic magnetic reconnection with the spectral index range of the turbulence from 8/3 to 3.0. The H-GRB spectra originate from the inverse turbulent cascade with the spectral index range of the turbulence from 2.0 to 3.5 that occurred during the large lengthscale magnetic reconnection. Thus, the GRB radiative spectra are diversified because the turbulent cascade modifies the turbulent energy spectrum. More observational samples are expected in the future to further identify our suggestions.