Gamma-ray bursts afterglow physics and the VHE domain

TL;DR

This paper reviews gamma-ray burst afterglow physics, emphasizing recent observations of very high energy emissions above 100 GeV, and discusses how upcoming CTA observations will enhance understanding of these phenomena.

Contribution

It provides a comprehensive review of current models, recent detections of VHE emissions, and discusses future prospects with CTA to improve understanding of GRB afterglows.

Findings

Detection of afterglow emission above 100 GeV by MAGIC and H.E.S.S.

Current models have limitations and open issues in explaining VHE emissions.

Future CTA observations are expected to significantly advance the understanding of GRB afterglow physics.

Abstract

Afterglow radiation in gamma-ray bursts (GRB), extending from the radio band to GeV energies, is produced as a result of the interaction between the relativistic jet and the ambient medium. Although in general the origin of the emission is robustly identified as synchrotron radiation from the shock-accelerated electrons, many aspects remain poorly constrained, such as the role of inverse Compton emission, the particle acceleration mechanism, the properties of the environment and of the GRB jet itself. The extension of the afterglow emission into the TeV band has been discussed and theorized for years, but has eluded for a long time the observations. Recently the Cherenkov telescopes MAGIC and H.E.S.S. have unequivocally proven that afterglow radiation is produced also above $100$\,GeV, up to at least a few TeV. The accessibility of the TeV spectral window will largely improve with the upcoming facility CTA ({the} Cherenkov Telescope Array). In this review article, we first revise the current model for afterglow emission in GRBs, its limitations and open issues. Then we describe the recent detections of very high energy emission from GRBs and the origin of this radiation. Implications on the understanding of afterglow radiation and constraints on the physics of the involved processes will be deeply investigated, showing how future observations, especially {by} the CTA Observatory, are expected to give a key contribution in improving our comprehension of such elusive sources.