GeV Emission from Prompt and Afterglow Phases of Gamma-Ray Bursts

TL;DR

This paper analyzes GeV gamma-ray emission from GRBs during prompt and afterglow phases, using EGRET data to test synchrotron self-Compton models and predict detection rates for GLAST, also estimating GRBs' contribution to the gamma-ray background.

Contribution

It provides the first detailed comparison of EGRET data with synchrotron self-Compton models for both phases and predicts GLAST detection rates based on these models.

Findings

EGRET constraints align with synchrotron self-Compton models.

GLAST expected to detect >20 GRBs per year in GeV range.

GRBs contribute at least 0.01% to the extragalactic gamma-ray background.

Abstract

We investigate the GeV emission from gamma-ray bursts (GRBs), using the results from the Energetic Gamma Ray Experimental Telescope (EGRET), and in view of the Gamma-ray Large Area Space Telescope (GLAST). Assuming that the conventional prompt and afterglow photons originate from synchrotron radiation, we compare an accompanying inverse-Compton component with EGRET measurements and upper limits on GeV fluence, taking Klein-Nishina feedback into account. We find that EGRET constraints are consistent with the theoretical framework of the synchrotron self-Compton model for both prompt and afterglow phases, and discuss constraints on microphysical parameters in both phases. Based on the inverse-Compton model and using EGRET results, we predict that GLAST would detect GRBs with GeV photons at a rate >~20 yr^{-1} from each of the prompt and afterglow phases. This rate applies to the high-energy tail of the prompt synchrotron emission and to the inverse-Compton component of the afterglow. Theory predicts that in a large fraction of the cases where synchrotron GeV prompt emission would be detected by GLAST, inverse-Compton photons should be detected as well at high energies >~10 GeV. Therefore GLAST will enable a more precise test of the high-energy emission mechanism. Finally, we show that the contribution of GRBs to the flux of the extragalactic gamma-ray background measured with EGRET is at least 0.01% and likely around 0.1%.