Thermal emission signatures in non-thermal blazars
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Abstract
Blazars, a subclass of active galactic nuclei with powerful relativistic plasma jets, are
among the most luminous and violently variable objects in the universe. They emit
radiation across the entire electromagnetic spectrum, and often change in brightness
over the course of hours or days. Different emission mechanisms are necessary in order
to explain the observed flux in different frequency ranges. In the ultraviolet-optical-
infrared regime these include components that arise from: 1) polarized synchrotron
radiation emanating from a powerful parsec-scale jet flowing from near the central
accreting black hole, 2) a multi-temperature accretion disk emitting thermal radia-
tion, and 3) an optically thick dusty torus located several parsecs from the central
engine that absorbs and re-emits, at infrared wavelengths, radiation originating in
the accretion disk. The goal of this study is to determine the relative importance
of these spectral components in the spectra of blazars. I use data from the Spitzer
Space Telescope in order to search for the presence of the dusty torus surrounding
four blazars, as well as to determine its luminosity and temperature. In two of the
observed sources, 1222+216 and CTA102, I determine that the torus can be modeled
as a 1200 K blackbody emitting at nearly 10 46 erg s −1 . Furthermore, I determine
the relative variability of the accretion disk of a sample of blazars by using spec-
tropolarimetry observations to separate the optical-UV spectrum into a polarized
viiicomponent, consisting of radiation described by a power-law F ν ∝ ν −α , and an ac-
cretion disk which consists of a thin disk described by the power-law F disk ∝ ν 1/3
plus a hot-spot of variable temperature. The spectra of several blazars are explained
by a version of this model in which the thin disk component is held constant, while
the blackbody varies on timescales of approximately years resulting with a flux of
the blackbody component comparable to the power-law disk component. I find that
variations in the emission from the hot-spot occurs approximately within 100 days
of γ-ray variations.
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Attribution-NoDerivatives 4.0 International