The AGILE observations of the hard and bright GRB 100724B

TL;DR

This paper analyzes the brightest gamma-ray burst detected by AGILE, GRB 100724B, highlighting its simultaneous MeV and GeV emissions, spectral evolution, and discussing its features within the context of recent gamma-ray burst models.

Contribution

The paper provides a detailed analysis of GRB 100724B's gamma-ray data and compares its features with other GRBs, offering insights into its emission mechanisms and spectral evolution.

Findings

Simultaneous MeV and GeV emissions without delay

Significant spectral evolution in hard X-rays

Comparison with other gamma-ray bursts and models

Abstract

The observation of Gamma Ray Bursts (GRBs) in the gamma-ray band has been advanced by the AGILE and Fermi satellites after the era of the Compton Gamma-Ray Observatory. AGILE and Fermi are showing that the GeV-bright GRBs share a set of common features, particularly the high fluence from the keV up to the GeV energy bands, the high value of the minimum Lorentz factor, the presence of an extended emission of gamma-rays, often delayed with respect to lower energies, and finally the possible presence of multiple spectral components. GRB 100724B, localised in a joint effort by Fermi and the InterPlanetary Newtork, is the brightest burst detected in gamma-rays so far by AGILE. Characteristic features of GRB 100724B are the simultaneous emissions at MeV and GeV, without delayed onset nor time lag as shown by the analysis of the cross correlation function, and the significant spectral evolution in hard X-rays over the event duration. In this paper we show the analysis of the AGILE data of GRB 100724B and we discuss its features in the context of the bursts observed so far in gamma-rays and the recently proposed models.