Total SEDs of the three scenarios and sensitivity curves of several ground- and space-based telescopes, assuming a distance to the source of ∼3 Mpc. We plot with solid, dashed, and dot-dashed lines the total SEDs of scenarios ζ₁, ζ₂, and ζ₃. The sensitivities of ALMA, VLA, and ngVLA are adapted from Guo et al. (2020) (1 h on-source integration); the SKA1 and SKA2 sensitivities are taken from Wang et al. (2024) (1 h); the sensitivities of XMM-Newton (10⁵ s), Chandra (10⁵ s), NuStar (10⁶ s), Fermi (10 yr), and CTA (50 h) are taken from Lucchetta et al. (2022) and references therein (the integration time for observations is given in brackets).