SED of the WR–WR binary Apep as modelled by del Palacio et al. (2022) for different fractions of the magnetic field energy density. It includes synchrotron emission and thermal bremsstrahlung (dashed lines), IC radiation (dot-dashed lines), and π⁰ decay (dotted lines). The total differential flux is represented by the solid lines, leaving out further IR, optical, and X-ray thermal components. In black, one can see the observational constraints set by the Australia Telescope Compact Array (ATCA, Callingham et al. 2019), the XMM-Newton X-ray observatory (del Palacio et al. 2022), and Fermi-LAT (this work). The high frequency-radio (19.7 GHz) and X-ray (3–10 keV) constraints are represented as upper limits given the presence (or possible existence for radio) of thermal components. Together with the ATCA limits, our SED results are compatible with 0.01 ≲ η_B ≲ 0.03 (i.e. 0.13 G ≲ B ≲ 0.27 G), which is consistent with the limits derived from the integrated photon flux.