A Spectral Analysis of Fermi-LLE GRBs

TL;DR

This paper conducts a detailed time-resolved spectral analysis of 36 Fermi-detected gamma-ray bursts, examining spectral parameters and their correlations, and investigates the physical origins of observed correlations through simulations.

Contribution

It provides a systematic analysis of spectral evolution in GRBs and clarifies the physical versus non-physical origins of parameter correlations.

Findings

Time-resolved spectra fit well with the Band function.

Identified correlations between $E_{p}$, $eta$, and flux.

Simulations show some correlations are due to selection effects.

Abstract

The prompt emission of gamma-ray bursts remains mysterious since the mechanism is difficult to understand even though there are much more observations with the development of detection technology. But most of the gamma-ray bursts spectra show the Band shape, which consists of the low energy spectral index $\alpha$, the high energy spectral index $\beta$, the peak energy $E_{p}$ and the normalization of the spectrum. We present a systematic analysis of the spectral properties of 36 GRBs, which were detected by the Gamma-ray Burst Monitor (GBM), simultaneously, were also observed by the Large Area Telescope (LAT) and the LAT Low Energy (LLE) detector on the $Fermi$ satellite. We performed the detailed time-resolved spectral analysis for all of the bursts in our sample. We found that the time-resolved spectrum at peak flux can be well fitted by the empirical Band function for each burst in our sample. Moreover, the evolution patterns of $\alpha$ and $E_{p}$ have been carried for statistical analysis, and the parameter correlations have been obtained such as $E_{p}-F$, $\alpha-F$, and $E_{p}- \alpha$, all of them are presented by performing the detailed time-resolved spectral analysis. We also demonstrated that the two strong positive correlations $\alpha-F$ and $E_{p}-\alpha$ for some bursts originate from a non-physical selection effects through simulation.