Impact of Observational and Modelling Assumptions on Intergalactic Magnetic Field Constraints from TeV Gamma-Ray Bursts with the Cherenkov Telescope Array Observatory

Abstract

The Intergalactic Magnetic Field (IGMF), permeating cosmic voids, is thought to be a relic of primordial magnetic fields generated in the early Universe and that gave rise to all astrophysical magnetic fields. While it has escaped direct detection, lower limits on its intensity can be derived by characterising the time-delayed secondary emission initiated when primary very high-energy (VHE) photons from gamma-ray bursts (GRBs) produce lepton pairs that are deflected by the IGMF before generating a secondary gamma-ray flux. Most current studies exclude IGMF values below $10^{-18}\;\mathrm{G}$, however, they are typically performed under idealised conditions. Focusing on the impact of modelling and observational choices, we simulate CTAO observations of GRBs 190114C and 221009A under varying conditions. For GRB 190114C-like sources, we establish a stable lower limit of $2\times10^{-16}\;\mathrm{G}$, robust against most variations in source properties and detection strategies. For more extreme GRB 221009A-like events, we demonstrate that CTAO could probe fields up to at least $10^{-16}\;\mathrm{G}$ under harsh conditions, improving significantly the current IGMF constraints.