2025ApJ...984...16H

We describe a postprocessing radiative transport code for computing the spectra, the core shift, and the surface-brightness distribution of special relativistic jets with arbitrary optical thickness. The jet consists of an electron-positron pair plasma and an electron-proton normal plasma. Electrons and positrons are relativistic and composed of thermal and nonthermal components, while protons are nonrelativistic and nonradiating. The fraction of a pair plasma, as well as the fraction of a nonthermal component, can be arbitrarily chosen. Only the synchrotron process is considered for emission and absorption when the radiative-transfer equation is integrated along our lines of sight. We describe a suite of test problems and confirm the frequency dependence of the core shift in the Konigl jet model when the plasma is composed of nonthermal components alone. Finally, we illustrate the capabilities of the code with model calculations, demonstrating that the jet will exhibit a limb-brightened structure in general when it is energized by the rotational energy of the black hole. It is also demonstrated that such limb-brightened jets show a ring-like structure in the brightness map when we observe the jet launching region nearly face-on.