Spectral Properties of Prompt Emission of Four Short Gamma-Ray Bursts Observed by the Suzaku-WAM and the Konus-Wind

TL;DR

This study jointly analyzes the spectral properties of four short gamma-ray bursts using Suzaku-WAM and Konus-Wind data, revealing high peak energies, spectral characteristics, and potential classification criteria.

Contribution

It provides the first broad-band spectral analysis of these short GRBs, highlighting spectral hardness and lag as key classification indicators.

Findings

Short GRBs have high E_peak around 1 MeV.

Spectral lag is consistent with zero for these GRBs.

No evidence of very large hardness ratios in the sample.

Abstract

We have performed a joint analysis of prompt emission from four bright short gamma-ray bursts (GRBs) with the Suzaku-WAM and the Konus-Wind experiments. This joint analysis allows us to investigate the spectral properties of short-duration bursts over a wider energy band with a higher accuracy. We find that these bursts have a high E$_{\rm peak}$, around 1 MeV and have a harder power-law component than that of long GRBs. However, we can not determine whether these spectra follow the cut-off power-law model or the Band model. We also investigated the spectral lag, hardness ratio, inferred isotropic radiation energy and existence of a soft emission hump, in order to classify them into short or long GRBs using several criteria, in addition to the burst duration. We find that all criteria, except for the existence of the soft hump, support the fact that our four GRB samples are correctly classified as belonging to the short class. In addition, our broad-band analysis revealed that there is no evidence of GRBs with a very large hardness ratio, as seen in the BATSE short GRB sample, and that the spectral lag of our four short GRBs is consistent with zero, even in the MeV energy band, unlike long GRBs. Although our short GRB samples are still limited, these results suggest that the spectral hardness of short GRBs might not differ significantly from that of long GRBs, and also that the spectral lag at high energies could be a strong criterion for burst classification.