Time resolved spectral analysis of the prompt emission of long gamma ray bursts with GeV Emission

TL;DR

This study conducts detailed time-resolved spectral analysis of bright long gamma-ray bursts with GeV emission, revealing consistent spectral features and correlations that shed light on the radiation mechanisms during prompt emission.

Contribution

It introduces a composite spectral model with two black bodies and a power law that fits multiple bright GRBs, highlighting common spectral evolution features.

Findings

Black body temperatures are strongly correlated.

Black body fluxes are strongly correlated.

Black body temperatures trace pulse profiles.

Abstract

We make a detailed time resolved spectroscopy of bright long gamma ray bursts (GRBs) which show significant GeV emissions (GRB 080916C, GRB 090902B, and GRB 090926A). In addition to the standard Band model, we also use a model consisting of a blackbody and a power-law to fit the spectra. We find that for the latter model there are indications for an additional soft component in the spectra. While previous studies have shown that such models are required for GRB 090902B, here we find that a composite spectral model consisting of two black bodies and a power law adequately fit the data of all the three bright GRBs. We investigate the evolution of the spectral parameters and find several generic interesting features for all three GRBs, like a) temperatures of the black bodies are strongly correlated to each other, b) flux in the black body components are strongly correlated to each other, c) the temperatures of the black body trace the profile of the individual pulses of the GRBs, and d) the characteristics of the power law component like the spectral index and the delayed onset bear a close similarity to the emission characteristics in the GeV regions. We discuss the implications of these results to the possibility of identifying the radiation mechanisms during the prompt emission of GRBs.