Gamma-ray bursts, the most luminous electromagnetic events in the universe, continue to challenge our understanding of extreme astrophysical phenomena, and recent observations of GRB 221009A have revealed unexpectedly bright, very-high-energy emissions. T. Mondal, S. Razzaque, J. C. Joshi, and colleagues investigate the origins of this exceptional burst, modelling its afterglow with a novel approach that considers a Gaussian structured jet expanding into a uniform medium. This work addresses a key question in the field, explaining how such intense emissions arise without requiring unrealistically high energies, and importantly, predicts the associated neutrino flux detectable by next-generation telescopes. By modelling both gamma-ray and neutrino emissions, the team demonstrates that while GRB 221009A itself remains below current detection thresholds, future observations with instruments like the Cherenkov Telescope Array and IceCube Gen2, combined with a brighter, closer burst, will be crucial for finally confirming a long-predicted link between gamma-ray bursts and high-energy cosmic neutrinos.
GRB 221009A Initial Detections and Notices
A comprehensive review of research related to the exceptionally bright gamma-ray burst, GRB 221009A, and related high-energy phenomena has been compiled. This work details observations and theoretical models exploring the physics of gamma-ray bursts, cosmic rays, and the potential for multi-messenger astronomy. Researchers have analyzed these observations to understand the burst’s extreme luminosity and rapid variability, revealing insights into the processes driving these energetic events. Theoretical investigations explore the mechanisms responsible for gamma-ray burst emission, including internal shock models, synchrotron self-Compton emission, and the role of magnetic fields.
Studies also examine the potential for detecting neutrinos from gamma-ray bursts, as these particles could provide crucial information about the burst’s origin and the acceleration of cosmic rays. Researchers have developed sophisticated simulations to predict the expected neutrino flux and assess the feasibility of detection with current and future neutrino telescopes. This compilation includes studies focusing on specific aspects of gamma-ray burst emission, such as the effects of Klein-Nishina effects and the role of hadronic interactions. This work addresses limitations in traditional models, which struggle to account for the observed luminosity without invoking unrealistically high energies. Researchers employed a Gaussian structured jet framework, moving beyond the assumption of uniform energy distribution within the jet. This framework naturally accounts for the evolution of the afterglow through synchrotron self-Compton emission, the primary mechanism responsible for observed sub-TeV photons.
The study models the interaction between the relativistic ejecta of the burst and a uniform interstellar medium, utilizing a forward-shock scenario. Researchers defined the jet energy distribution with a Gaussian profile, where energy decreases with distance from the jet core. This profile naturally explains the temporal evolution of the afterglow, avoiding the need for extreme energy values. The initial velocity of the jet also follows a Gaussian profile, further refining the model’s accuracy. By accurately simulating the afterglow, scientists constrained the jet structure, radiation mechanisms, and particle acceleration processes.
This detailed approach provides a more realistic representation of the complex physical processes occurring within the burst environment. Furthermore, the study predicts the corresponding neutrino flux, crucial for multi-messenger astronomy. While the predicted flux for GRB 221009A falls below current detector sensitivities, future observations with advanced telescopes may reveal these elusive particles.
TeV Emission and Neutrino Constraints from GRB 221009A
Recent observations of very-high-energy emission from gamma-ray burst afterglows, notably GRB 221009A, reveal emission exceeding predictions from standard models. This suggests contributions from synchrotron self-Compton processes and potentially hadronic interactions. Scientists modelled the afterglow using a Gaussian structured jet interacting with a uniform medium, successfully reproducing the observed emission without requiring unrealistically high energies. The analysis also places constraints on the physical properties of the burst by examining the lack of coincident neutrino detections. Researchers investigated the corresponding neutrino flux in the PeV-EeV energy range, deriving a time-integrated upper limit based on the effective areas of future neutrino telescopes.
Comparisons between on-axis and off-axis viewing geometries reveal that jet orientation significantly impacts the predicted neutrino signal strength. These studies demonstrate that a brighter and closer burst than GRB 221009A would be crucial for any neutrino detections. The research utilizes a Gaussian structured jet model, where the jet energy distribution follows a Gaussian profile, naturally accounting for the temporal evolution of the afterglow. The model predicts a gradual steepening of the afterglow light curve, consistent with observations. Scientists successfully reproduced the observed very-high-energy afterglow using a model of a Gaussian structured jet expanding into a uniform medium, accurately capturing both the spectral and temporal characteristics of the burst. The analysis indicates that the observed emission is likely dominated by synchrotron self-Compton processes, requiring a mildly off-axis jet structure and a significantly higher energy output than typical bursts. Researchers calculated the expected neutrino flux generated through proton-gamma interactions within the burst environment, considering the effects of neutrino oscillation during their journey to Earth.
Comparisons between on-axis and off-axis viewing angles reveal substantial variations in predicted neutrino signals. Despite optimistic calculations, the study suggests that detecting neutrinos from GRB 221009A with current or near-future telescopes remains challenging.
👉 More information
🗞 Multi Messenger Study of GRB 221009A with VHE Gamma-ray and Neutrino Afterglow from a Gaussian Structured Jet
🧠ArXiv: https://arxiv.org/abs/2511.13633