Constraining Emission Models of Luminous Blazar Sources

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 KleinNishina 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.

Search for the shortest variability at gamma rays in flat-spectrum radio quasars

“…On one side, there is a group of researchers supporting the hypothesis that the γ rays in the sources powered by the EC process are generated by the interaction with seed photons from the molecular torus (infrared photons), which is placed at some parsecs from the central engine (e.g. Abdo et al 2010c;Marscher et al 2008Marscher et al , 2010Sikora et al 2009). On the other side, another group of researchers is instead favoringwith different arguments -the hypothesis of a dissipation inside the BLR, i.e.…”

Modelling the multi-wavelength emission of flat-spectrum radio quasar 3C 279

“…The external radiation fields in the jet comoving frame by Maxwellian distribution peaked at photon energies EBLR ∼ 10 eV × Γ and EIR ∼ 0.3 eV × Γ. In our calculation, we adopt the radiation density profile βBLR = 3 (Sikora et al 2009) and βIR = 4 (Hayashida et al 2012), respectively. Because the initial γ-ray emission site that is defined by x = 0 in the model does not show the real distance between the core and base of jet, we introduce another parameter LB to describe it in the fluid frame.…”

MULTIWAVELENGTH STUDY OF QUIESCENT STATES OF Mrk 421 WITH UNPRECEDENTED HARD X-RAY COVERAGE PROVIDED BY NuSTAR IN 2013

“…The cross-correlation of time series measured in various bands provides additional clues to the radiative processes, the acceleration and energy distribution of radiating particles, and the structure and intrinsic power of the relativistic jet. The relative temporal variability in different spectral bands, from radio through VHE γ-rays, provides an important handle on the location of the energy dissipation with respect to the central black hole (Sikora et al 2009;Janiak et al 2012). In the context of a specific model for the radiation, the underlying particle distributions may be determined more or less directly from the observed multiwavelength SEDs.…”