GeV emission from Gamma-Ray Burst afterglows

TL;DR

This paper predicts various GeV emission mechanisms from GRB afterglows, emphasizing the detectability of self-Compton and inverse-Compton processes by LAT, and discusses how spectral and temporal features can identify the emission origins.

Contribution

It introduces new models for GeV afterglow emission involving pair-enriched outflows and inverse-Compton scattering, expanding understanding of high-energy GRB afterglows.

Findings

LAT can detect self-Compton emission from forward shocks.

Inverse-Compton scattering by pair-enriched outflows produces detectable GeV emission.

Spectral and decay measurements can identify emission mechanisms.

Abstract

We calculate the GeV afterglow emission expected from a few mechanisms related to GRBs and their afterglows. Given the brightness of the early X-ray afterglow emission measured by Swift/XRT, GLAST/LAT should detect the self-Compton emission from the forward-shock driven by the GRB ejecta into the circumburst medium. Novel features discovered by Swift in X-ray afterglows (plateaus and chromatic light-curve breaks) indicate the existence of a pair-enriched, relativistic outflow located behind the forward shock. Bulk and inverse-Compton upscattering of the prompt GRB emission by such outflows provide another source of GeV afterglow emission detectable by LAT. The large-angle burst emission and synchrotron forward-shock emission are, most likely, too dim at high photon energy to be observed by LAT. The spectral slope of the high-energy afterglow emission and its decay rate (if it can be measured) allow the identification of the mechanism producing the GeV transient emission following GRBs.