Prospects for detection of very high-energy emission from GRB in the context of the external shock model

TL;DR

This paper assesses the potential for detecting very high-energy gamma-ray emission from GRBs using MAGIC, focusing on early X-ray flares and afterglow phases within the external shock model, and proposes optimized observational strategies.

Contribution

It provides detailed predictions of high-energy emission from GRBs in the external shock scenario and outlines observational strategies for MAGIC to detect these signals.

Findings

X-ray flares with average properties can be detected at z<0.7 in the 100 GeV range.

Late afterglow emission detection is feasible for z<0.5 if external medium density exceeds a few cm^-3.

Optimal observation windows are 10-20 s after burst for flares and up to 20 ks for afterglow detection.

Abstract

The detection of the 100 GeV-TeV emission by a gamma-ray burst (GRB) will provide an unprecedented opportunity to study the nature of the central engine and the interaction between the relativistic flow and the environment of the burst's progenitor. In this paper we show that there are exciting prospects of detecting from the burst by MAGIC high-energy (HE) emission during the early X-ray flaring activity and, later, during the normal afterglow phase. We also identify the best observational strategy, trigger conditions and time period of observation. We determine the expected HE emission from the flaring and afterglow phases of GRBs in the context of the external shock scenario and compare them with the MAGIC threshold. We find that an X-ray flare with the average properties of the class can be detected in the 100 GeV range by MAGIC, provided that z<0.7. The requested observational window with MAGIC should then start from 10-20 s after the burst and cover about 1000-2000 s. Furthermore, we demonstrate that there are solid prospects of detecting the late afterglow emission in the same energy range for most of the bursts with z<0.5 if the density of the external medium is n> a few cm^-3. In this case, the MAGIC observation shall extend to about 10-20 ks. We provide recipes for tailoring this prediction to the observational properties of each burst,in particular the fluence in the prompt emission and the redshift, thus allowing an almost real time decision procedure to decide whether to continue the follow-up observation of a burst at late times.