Comptonization of Infrared Radiation from Hot Dust by Relativistic Jets in Quasars

Abstract

We demonstrate the importance of near-infrared radiation from hot dust for Compton cooling of electrons/positrons in quasar jets. In our model, we assume that the non-thermal radiation spectra observed in OVV quasars are produced by relativistic electrons/positrons accelerated in thin shells which propagate down the jet with relativistic speeds. We show that the Comptonization of the near-IR flux is likely to dominate the radiative output of OVV quasars in the energy range from tens of keV up to hundreds of MeV, where it exceeds that produced by Comptonization of the UV radiation reprocessed and rescattered in the Broad Emission Line region. The main reason for this lies in the fact that the jet encounters the ambient IR radiation over a relatively large distance as compared to the distance where the energy density of the broad emission line light peaks. In the soft - to mid energy X-ray band, the spectral component resulting from Comptonization of the near-IR radiation joins smoothly with the synchrotron-self-Compton component, which may be responsible for the soft X-ray flux. At the highest observed gamma-ray energies, in the GeV range, Comptonization of broad emission lines dominates over other components.Comment: 23 pages, including 5 Postscript figures and 3 tables, uses aastex. Astrophysical Journal, accepted for publication in the December 20, 2000 issu