Flux of photons produced by synchrotron emission for a filament observed from the directions forming the indicated angles with its axis. The filament is located at 100 Mpc and harbors a source that injects a pure proton composition with (isotropic) luminosity of L_E,19 = 10⁴² erg/s and a spectral index of 2.3. The four panels represent various models of magnetic fields. From left to right: “anisotropic” with B₀ = 0.1   nG, “anisotropic” with B₀ = 1   nG, “isotropic” with B₀ = 1   nG, and “contrasted” with B₀ = 1   nG.