Method for Organizing the Multiwavelength Data of Radio-Loud Active Galactic Nuclei

Abstract

The broadband emission observed from radio galaxies, BL Lac objects and quasars is thought to be produced by energetic electrons confined in plasma blobs which are ejected from supermassive black holes at relativistic speeds. The lower energy radio-through-optical component is almost certainly nonthermal electron synchrotron radiation, while the higher-energy $γ$-ray component is probably due to Compton scattering of target photons by these same electrons. If the high-energy component is formed by jet electrons Compton-scattering radiation from outside the jet, such as the direct or rescattered accretion-disk photons, then the ratio of the power in the high-energy Compton component to the power in the low-energy synchrotron component stands in a simple relation depending on the observing angle to the jet and the plasma outflow speed. When combined with contemporaneous VLBI measurements of apparent transverse speed, we find that a simple diagram relates different classes of radio-loud active galactic nuclei (AGNs) and makes definite predictions for multiwavelength observations of these sources. If an equipartition parameter remains constant between episodes of plasma ejection, then multiple observations of a single source can in principle determine the Hubble constant.