Helical jets in blazars. Interpretation of the multifrequency long-term variability of AO 0235+16

TL;DR

This paper models the long-term multiwavelength variability of blazar AO 0235+16 using a helical jet framework, explaining periodic and non-periodic emission features through jet orientation changes and instabilities.

Contribution

It applies a helical jet model to interpret the complex variability of AO 0235+16, linking observed emission patterns to jet orientation and flow instabilities.

Findings

Helical jet rotation explains periodic radio and optical outbursts.

Model accounts for broad-band spectral energy distribution variability.

Flow instabilities explain non-periodic emission features.

Abstract

The long-term variability of the multiwavelength blazar emission can be interpreted in terms of orientation variations of a helical, inhomogeneous, non-thermally emitting jet, possibly caused by the orbital motion of the parent black hole in a binary system (Villata & Raiteri 1999). The helical-jet model is here applied to explain the quasi-periodic radio-optical light curves and the broad-band spectral energy distributions (SEDs) of the BL Lac object AO 0235+16. Through a suitable choice of the model parameters, the helix rotation can well account for the periodicity of the main radio and optical outbursts and for the corresponding SED variability, while the interspersed minor radio events could be interpreted as due either to some local distortions of the helical structure or to other phenomena contributing to the source emission. In particular, the probable existence of flow instabilities provides a viable interpretation for the non-periodic features.