Περίληψη:
Context. As a subcategory of active galactic nuclei, blazars are
distinguished by their non-thermal variable emission. This emission
extends over the whole electromagnetic spectrum and is a consequence of
particle acceleration inside their relativistic jets. However, an open
question remains regarding the relation of radio emission compared to
that of higher frequencies. Aims. Observations of blazar emission show
that the location of radio might be very different from the one where
the rest of the spectrum is produced and, thus, often requires separate
modeling. We aim to produce both types of emission within the context of
a single model. Methods. We constructed a self-consistent one-zone
expanding leptonic model for studying the connection between the radio
emission and the emission at higher frequencies. We then applied it to
the flaring states of blazars. Assuming an accelerating episode as the
source moves down the jet and expands, we numerically studied the
electron evolution as they lose energy due to adiabatic expansion and
synchrotron or inverse Compton radiation. Results. We find that
high-frequency radiation mimics the electron injection and is mainly
produced close to the acceleration site where cooling is strong. In
contrast, the radio emission is produced further down the jet when the
emitting region has become optically thin with regard to synchrotron
self-absorption due to expansion. We briefly present the role of the
initial parameters, such as the magnetic field strength, the electron
luminosity, and expansion velocity, on the localization of the radio
emission site. We show that the expanding one-zone model is inherently
different from the non-expanding one and, in addition, it requires more
parameters. For example, we apply our approach to the observational data
of a Mrk 421 gamma-ray and radio flare observed in 2013.
