Constraining emission models of luminous blazar sources

M Sikora, Ł Stawarz, R Moderski… - The Astrophysical …, 2009 - iopscience.iop.org
M Sikora, Ł Stawarz, R Moderski, K Nalewajko, GM Madejski
The Astrophysical Journal, 2009iopscience.iop.org
Many luminous blazars which are associated with quasar-type active galactic nuclei display
broadband spectra characterized by a large luminosity ratio of their high-energy (γ-ray) and
low-energy (synchrotron) spectral components. This large ratio, reaching values up to 100,
challenges the standard synchrotron self-Compton models by means of substantial
departures from the minimum power condition. Luminous blazars also typically have very
hard X-ray spectra, and those in turn seem to challenge hadronic scenarios for the high …
Abstract
Many luminous blazars which are associated with quasar-type active galactic nuclei display broadband spectra characterized by a large luminosity ratio of their high-energy (γ-ray) and low-energy (synchrotron) spectral components. This large ratio, reaching values up to 100, challenges the standard synchrotron self-Compton models by means of substantial departures from the minimum power condition. Luminous blazars also typically have very hard X-ray spectra, and those in turn seem to challenge hadronic scenarios for the high-energy blazar emission. As shown in this paper, no such problems are faced by the models which involve Comptonization of radiation provided by a broad-line region, or dusty molecular torus. The lack or weakness of bulk-Compton and Klein–Nishina features indicated by the presently available data favors the production of γ-rays via upscattering of infrared photons from hot dust. This implies that the blazar emission zone is located at parsec-scale distances from the nucleus, and as such is possibly associated with the extended, quasi-stationary reconfinement shocks formed in relativistic outflows. This scenario predicts characteristic timescales for flux changes in luminous blazars to be days/weeks, consistent with the variability patterns observed in such systems at infrared, optical, and γ-ray frequencies. We also propose that the parsec-scale blazar activity can be occasionally accompanied by dissipative events taking place at sub-parsec distances and powered by internal shocks and/or reconnection of magnetic fields. These could account for the multiwavelength intraday flares occasionally observed in powerful blazar sources.
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