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Very-high-energy afterglows from Gaussian structured jets in wind-driven media and prospects for the CTA detectability of events like GRB 221009A

Tanima Mondal1,*, Sabyasachi Chakraborty1, Lekshmi Resmi2, and Debanjan Bose3

  • *Contact author: mtanima14@gmail.com
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Phys. Rev. D 114, 063027 – Published 10 September, 2026

DOI: https://doi.org/10.1103/yvg8-t64l

Abstract

Recent detections of very-high-energy [(VHE) ≳100  GeV] photons from afterglows like gamma-ray burst (GRB) 221009A demand models that treat jet angular structure, circumburst stratification, and inverse Compton radiation self-consistently. We present a numerical afterglow framework in which a Gaussian structured jet decelerates as an adiabatic forward shock in a wind-stratified medium (ρ∝r−2), and compute broadband synchrotron and synchrotron self-Compton (SSC) emission. Our approach aims to connect a wind-stratified environment with a Gaussian angular jet profile and to explore SSC emission to predict VHE afterglow detectability with the Cherenkov Telescope Array (CTA). We find that the TeV peak time and peak flux are primarily governed by jet geometry (ratio of θv/θc), together with wind-driven blast-wave deceleration and jet microphysics. In particular, variations in the jet kinetic energy (Ek), wind density parameter (A⋆), and the ratio of microphysical parameters (εe and εB) can change the TeV flux by orders of magnitude. Using the CTAO North differential sensitivity at 250 GeV, we simulate 4×104 wind-Gaussian afterglows and find that only ∼10% satisfy our detectability criterion, primarily for bursts with high Ek, moderate to high A⋆, high εe, and low εB, and near on-axis jet geometries (θv/θc≲2). Finally, fitting the multiband afterglow of GRB 221009A from radio to TeV, we obtain a mildly off-axis, SSC-dominated afterglow in a wind-driven medium that reproduces the observed broadband temporal evolution. The inferred parameters favor strong TeV SSC emission, implying that GRBs similar to GRB 221009A should be detectable by CTA.

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Phys. Rev. D 114, 063027– Published 10 September, 2026
  • Received 6 March 2026
  • Accepted 21 July 2026
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