LEARNING ABOUT ACTIVE GALACTIC NUCLEUS JETS FROM PROPERTIES OF BLAZARS

We use multiwavelength spectra of core-dominated hat spectrum radio-lo ud quasars (FSRQs) to study properties of jets in active galactic nucl ei. From a comparison of the predicted bulk Compton radiation with the observed soft X-ray fluxes, we find that these jets must be optically very thin. This eliminates the importance of such processes as Coulom b interactions, pair annihilation, and bremsstrahlung and determines t he minimum distance from the black hole where a powerful jet can be fu lly developed (accelerated, collimated, and mass loaded). In the case of pair dominated jets, this distance is much greater than 100GM(BH)/c (2). Further constraints on the parameters of a jet can be derived fro m luminosities and positions of spectral peaks of low-energy (IR/optic al) and high-energy (gamma-ray) radiation components, provided that bo th are produced by the same population of electrons. Whereas there app ears to be a consensus about the synchrotron origin of the low-energy component, there is still debate about the mechanism of production of gamma-rays. Most likely, they result from Comptonization of a soft rad iation field by the same electrons that produce synchrotron radiation. Such a soft radiation field can be provided by the synchrotron proces s in a jet, by the accretion disk, and by a fraction of the disk radia tion that is reprocessed/ rescattered by emission line clouds, dust, a nd intercloud medium. We show that for FSRQs, the production of the hi gh-energy radiation can be dominated by Comptonization of synchrotron radiation only for jets with moderate bulk Lorentz factors Gamma(j) (l ess than or similar to 3) or if external radiation fields are much wea ker than those observed in typical quasars. Furthermore, in synchrotro n self-Compton (SSC) models, the relativistic plasma producing nonther mal radiation is constrained to be very weakly magnetized (B' < 0.01 g auss) and located at very large distances (r similar to 10(19) cm). Th ese can impose problems with jet confinement and with short observed t imescale of variability. In the external radiation Compton (ERC) model s, the magnetic fields are predicted to be much stronger (B' similar t o 100 gauss), and nonthermal radiation can be produced very closely to the black hole (r similar to 10(16) cm), which alleviates the problem s with plasma confinement and short timescale variability. However, be cause of the close proximity to the black hale, the constraints impose d by the bulk Compton radiation imply that the plasma must be free of e(+)e(-) pairs. Finally, we discuss the difficulties that existing mod els have in explaining the sharp spectral breaks at MeV energies and p ostulate a ''hot electron'' version of the ERC scenario for the produc tion of MeV peaks. We show that appropriate electron ''temperatures'' (kT similar to 100 MeV) to produce the luminosity peak at MeV energies by Comptonization of external UV radiation are achievable at subparse c distances only for proton-electron plasmas.