Gamma-Ray Bursts at TeV Energies: Theoretical Considerations

Abstract

Gamma-ray bursts (GRBs) are the most luminous explosions in the Universe and are powered by ultra-relativistic jets. Their prompt γ-ray emission briefly outshines the rest of the γ-ray sky, making them detectable from cosmological distances. A burst is followed by, and sometimes partially overlaps with, a similarly energetic but very broadband and longer-lasting afterglow emission. While most GRBs are detected below a few MeV, over 100 have been detected at high (≳0.1 GeV) energies, and several have now been observed up to tens of GeV with the Fermi Large Area Telescope (LAT). A new electromagnetic window in the very-high-energy (VHE) domain (≳0.1 TeV) was recently opened with the detection of an afterglow emission in the (0.1–1)TeV energy band by ground-based imaging atmospheric Cherenkov telescopes. The emission mechanism for the VHE spectral component is not fully understood, and its detection offers important constraints for GRB physics. This review provides a brief overview of the different leptonic and hadronic mechanisms capable of producing a VHE emission in GRBs. The same mechanisms possibly give rise to the high-energy spectral component seen during the prompt emission of many Fermi-LAT GRBs. Possible origins of its delayed onset and long duration well into the afterglow phase, with implications for the emission region and relativistic collisionless shock physics, are discussed. Key results for using GRBs as ideal probes for constraining models of extra-galactic background light and intergalactic magnetic fields, as well as for testing Lorentz invariance violation, are presented.

Jet Structure and Burst Environment of GRB 221009A

“…In recent years, IACTs have successfully detected the VHE afterglows of several GRBs, such as GRBs 180720B (0.1-0.4 TeV; Abdalla et al 2019), 190114C (0.3-1 TeV;MAGIC Collaboration et al 2019), 190829A (0.2-4 TeV; H. E. S. S. Collaboration et al 2021), 201015A (>140 GeV; Suda et al 2021), and 201216C (70-200 GeV;MAGIC Collaboration et al 2022Abe et al 2023), thereby extending the detection range to the sub-TeV to TeV energy range. This achievement represents the final missing element in the broadband radiation spectrum of GRB afterglows, signifying the arrival of the TeV era in the field of GRBs and ushering in an era of new discoveries and cognitive breakthroughs (Nava 2021;Berti & Carosi 2022;Gill & Granot 2022;Miceli & Nava 2022).…”

A Comprehensive Investigation of Gamma-Ray Burst Afterglows Detected by TESS

“…Gamma-ray bursts (GRBs) are the most powerful explosions we observe in the Universe, surpassing all other catastrophic events in terms of electromagnetic luminosity (Gill & Granot 2022). Peaking at gamma-ray wavelengths, these bursts release rapid jets of radiation that can carry more energy in the span of a few seconds than the Sun will in its entire 10 billion year lifetime (Fishman & Hartmann 1997).…”

External Inverse-compton and Proton Synchrotron Emission from the Reverse Shock as the Origin of VHE Gamma Rays from the Hyper-bright GRB 221009A

“…Gamma-ray bursts (GRBs) are among the most luminous explosions in the universe (Mészáros 2006;Kumar & Zhang 2014). In 2019, the detection of two TeV bursts, GRB 190114C (MAGIC Collaboration et al 2019;MAGIC Collaboration 2019) and GRB 180720B (Abdalla et al 2019), opened a new window in the very high-energy (VHE)(0.1 TeV) band for studying GRBs, providing us with new opportunities to investigate the nature of GRBs (see Gill &Granot 2022 andMiceli &Nava 2022 for reviews).…”