GRB980923. A burst with a short duration high energy component

TL;DR

This paper reports the discovery of a short-duration, high-energy spectral component in GRB980923, distinct from the prompt emission and tail, characterized by a power-law spectrum lasting about 2 seconds.

Contribution

It provides the first detailed analysis of a short, high-energy component in GRB980923, expanding understanding of spectral complexity in gamma-ray bursts.

Findings

Identification of a 2-second high-energy power-law component

Distinct evolution of high-energy component from prompt emission

Presence of three separate spectral components in GRB980923

Abstract

The prompt emission of Gamma Ray Bursts (GRBs) is usually well described by the Band function: two power-laws joined smoothly at a given break energy. In addition to the Band component, a few bursts (GRB941017, GRB090510, GRB090902B and GRB090926A) show clear evidence for a distinct high-energy spectral component, which in some cases evolves independently from the prompt keV component and is well described by a power-law (PL), sometimes with a cut-off energy; this component is found to have long duration, even longer than the burst itself for all the four bursts. Here we report the observation of an anomalous short duration high energy component in GRB980923. GRB980923 is one of the brightest Gamma-Ray Bursts (GRBs) observed by BATSE. Its light curve is characterized by a rapid variability phase lasting ~ 40 s, followed by a smooth emission tail lasting ~ 400 s. A detailed joint analysis of BATSE (LAD and SD) and EGRET TASC data of GRB980923 reveles the presence of an anomalous keV to MeV component in the spectrum that evolves independently from the prompt keV one. This component is well described by a PL with a spectral index of -1.44 and lasts only ~ 2 s; it represents one of the three clearly separated spectral components identified in GRB980923, the other two being the keV prompt emission, well described by the Band function and the tail, well fit by a Smoothly Broken Power Law (SBPL).