The observation of Gamma-Ray Bursts (GRBs) is confirmed as a fundamental tool not only for studying the most energetic sources in the Universe, but also for investigating the primordial Universe and intergalactic magnetic fields.

In this context, a recent study published in Physical Review D, involving researchers from INAF (Istituto Nazionale di Astrofisica), INFN (Istituto di Fisica Nucleare), and ASI (Agenzia Spaziale Italiana), has provided new evidence for the existence of primordial magnetic fields in cosmic voids. Among the authors are Da Vela, Longo, Saturni, and Stamerra, members of the ASTRI Mini-Array collaboration.

The result was made possible thanks to the observation of the Gamma-Ray Burst GRB 221009A with NASA’s Fermi Gamma-ray Space Telescope in the Giga-electronvolt (GeV) energy range, combined with ground-based measurements in the Tera-electronvolt (TeV) band performed by the Large High Altitude Air Shower Observatory (LHAASO), located in Tibet.

Gamma rays emitted by GRBs, while traveling across intergalactic space, interact with cosmic radiation fields, produce electron–positron pairs, and trigger an electromagnetic cascade. The deflection of these charged particles by intergalactic magnetic fields generates a delayed gamma-ray signal, observable at GeV energies compared to the emission detected at higher energies (in the TeV range). The minimum magnetic field strength measured in this way, equal to 25 billionths of a billionth of a gauss, represents the most stringent constraint obtained so far.