Expected high energy emission from GRB 080319B and origins of the GeV emission of GRBs 080514B, 080916C and 081024B

TL;DR

This paper models the high energy emission mechanisms in GRB 080319B and discusses the origins of GeV emissions in other GRBs, predicting detectable photon counts and durations for Fermi LAT and AGILE satellites.

Contribution

It provides detailed calculations of high energy emission sources in GRB 080319B and compares these with observations of other GRBs, supporting current emission models.

Findings

Hundreds of high energy photons expected for Fermi LAT

>10 GeV emission lasts twice as long as soft gamma-rays

Observations consistent with existing high energy emission models

Abstract

We calculate the high energy (sub-GeV to TeV) prompt and afterglow emission of GRB 080319B that was distinguished by a naked-eye optical flash and by an unusual strong early X-ray afterglow. There are three possible sources for high energy emission: the prompt optical and $\gamma$-ray photons IC scattered by the accelerated electrons, the prompt photons IC scattered by the early external reverse-forward shock electrons, and the higher band of the synchrotron and the synchrotron self-Compton emission of the external shock. There should have been in total {hundreds} high energy photons detectable for the Large Area Telescope (LAT) onboard the Fermi satellite, and {tens} photons of those with energy $> 10$ GeV. The $> 10$ GeV emission had a duration about twice that of the soft $\gamma$-rays. AGILE could have observed these energetic signals if it was not occulted by the Earth at that moment. The physical origins of the high energy emission detected in GRB 080514B, GRB 080916C and GRB 081024B are also discussed. These observations seem to be consistent with the current high energy emission models.