On Pair Content and Variability of Subparsec Jets in Quasars

Abstract

This paper reviews the topic of sub-parsec - scale jets in quasars, and covers the the following issues: observations of parsec and sub-parsec scale jets; energy dissipation and particle acceleration; radiative processes; magnetic fields, pair content, and energetics; and variability and its relation to the central engine activity. In particular, we describe how internal shocks can explain properties of gamma-ray flares and demonstrate that MeV blazars (those with luminosity peak in the 1-30 MeV range) can be unified with GeV blazars (those with luminosity peak at GeV energies) assuming that in GeV blazars the gamma-ray flares are produced via Comptonization of broad emission lines, whereas in the MeV blazars they result from Comptonization of infrared radiation of hot dust. We also make predictions about the radiative effects of bulk Compton process in the soft X-ray band and show how spectral and variability properties in that band can be used to constrain structure of jets near their bases.