A Comprehensive Study of Bright Fermi-GBM Short Gamma-Ray Bursts: II. Very Short Burst and Its Implications

TL;DR

This study analyzes ten very short gamma-ray bursts detected by Fermi-GBM, revealing common spectral features and moderate evidence of thermal components, which have implications for understanding GRB emission mechanisms and classifications.

Contribution

It provides a comprehensive spectral analysis of very short GRBs, identifying thermal components and their potential role in gamma-ray emission processes.

Findings

Moderate thermal component detection in 8 out of 10 GRBs.

Spectral features support short/hard versus long/soft classification.

Thermal components may significantly influence gamma-ray emission mechanisms.

Abstract

A thermal component is suggested to be the physical composition of the ejecta of several bright gamma-ray bursts (GRBs). Such a thermal component is discovered in the time-integrated spectra of several short GRBs as well as long GRBs. In this work, we present a comprehensive analysis of ten very short GRBs detected by Fermi Gamma-Ray Burst Monitor to search for the thermal component. We found that both the resultant low-energy spectral index and the peak energy in each GRB imply a common hard spectral feature, which is in favor of the main classification of the short/hard versus long/soft dichotomy in the GRB duration. We also found moderate evidence for the detection of thermal component in eight GRBs. Although such a thermal component contributes a small proportion of the global prompt gamma-ray emission, the modified thermal-radiation mechanism could enhance the proportion significantly, such as in subphotospheric dissipation.