AGILE detection of delayed gamma-ray emission from GRB 080514B

TL;DR

This paper reports the first detection of individual high-energy gamma-ray photons from GRB 080514B using the AGILE satellite, revealing extended emission beyond the initial burst and demonstrating the satellite's capability to study such phenomena.

Contribution

It presents the first clear detection of high-energy gamma-ray photons from a GRB with AGILE, showing extended emission and improved flux measurement due to low dead time.

Findings

Gamma-ray emission extends longer than X-ray emission.

AGILE/GRID's low dead time allows accurate flux assessment.

Gamma-ray to X-ray flux ratio varies between phases.

Abstract

GRB 080514B is the first gamma ray burst (GRB), since the time of EGRET, for which individual photons of energy above several tens of MeV have been detected with a pair-conversion tracker telescope. This burst was discovered with the Italian AGILE gamma-ray satellite. The GRB was localized with a cooperation by AGILE and the interplanetary network (IPN). The gamma-ray imager (GRID) estimate of the position, obtained before the SuperAGILE-IPN localization, is found to be consistent with the burst position. The hard X-ray emission observed by SuperAGILE lasted about 7 s, while there is evidence that the emission above 30 MeV extends for a longer duration (at least ~13 s). Similar behavior was seen in the past from a few other GRBs observed with EGRET. However, the latter measurements were affected, during the brightest phases, by instrumental dead time effects, resulting in only lower limits to the burst intensity. Thanks to the small dead time of the AGILE/GRID we could assess that in the case of GRB 080514B the gamma-ray to X-ray flux ratio changes significantly between the prompt and extended emission phase.