Oblique Shocks As The Origin Of Radio To Gamma-ray Variability In AGN

TL;DR

This paper revisits the shock in jet model for blazar variability, demonstrating that oblique shocks can explain polarization swings and are linked to gamma-ray activity, with implications for magnetic field structure.

Contribution

It introduces a generalized shock model with arbitrary orientation and magnetic field configurations, explaining polarization behavior and linking shocks to gamma-ray flares.

Findings

Oblique shocks can produce polarization swings less than 90 degrees.

Magnetic fields are likely predominantly random in quiescent states.

Shock events correlate with gamma-ray flaring activity.

Abstract

The `shock in jet' model for cm-waveband blazar variability is revisited, allowing for arbitrary shock orientation with respect to the jet flow direction, and both random and ordered magnetic field. It is shown that oblique shocks can explain events with swings in polarization position angle much less than the 90 deg. associated with transverse structures, while retaining the general characteristics of outbursts, including spectral behavior and level of peak percentage polarization. Models dominated by a force-free, minimum energy magnetic field configuration (essentially helical) display a shallow rise in percentage polarization and frequency dependent swing in polarization position angle not in agreement with the results of single-dish monitoring observations, implying that the field is predominantly random in the quiescent state. Outbursts well-explained by the `shock in jet' model are present during gamma-ray flaring in several sources, supporting the idea that shock events are responsible for activity from the radio to gamma-ray bands.