Gamma-Ray Bursts Above 1 GeV

TL;DR

This paper reviews high-energy gamma-ray observations of gamma-ray bursts above 1 GeV, discusses theoretical models, and highlights how future detections can help differentiate emission mechanisms and intervening effects.

Contribution

It provides a comprehensive summary of observations and models for GeV--TeV emission in gamma-ray bursts, emphasizing the potential of future detections to discriminate between scenarios.

Findings

High-energy photons (>100 MeV) have been detected from bright bursts.

High-energy emission may be common in gamma-ray bursts.

Future observations can distinguish between intrinsic spectral features and medium effects.

Abstract

One of the principal results obtained by the Compton Gamma Ray Observatory relating to the study of gamma-ray bursts was the detection by the EGRET instrument of energetic ($>$100 MeV) photons from a handful of bright bursts. The most extreme of these was the single 18 GeV photon from the GRB940217 source. Given EGRET's sensitivity and limited field of view, the detection rate implies that such high energy emission may be ubiquitous in bursts. Hence expectations that bursts emit out to at least TeV energies are quite realistic, and the associated target-of-opportunity activity of the TeV gamma-ray community is well-founded. This review summarizes the observations and a handful of theoretical models for generating GeV--TeV emission in bursts sources, outlining possible ways that future positive detections could discriminate between different scenarios. The power of observations in the GeV--TeV range to distinguish between spectral structure intrinsic to bursts and that due to the intervening medium between source and observer is also discussed.