Helical jets in blazars

Interpretation of the multifrequency long-term variability of AO 0235+16

¹ Landessternwarte Heidelberg-Königstuhl, Königstuhl 12, 69117 Heidelberg, Germany
² Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese (TO), Italy e-mail: [villata;raiteri]@to.astro.it

Corresponding author: L. Ostorero, l.ostorero@lsw.uni-heidelberg.de

Received: 5 December 2003
Accepted: 10 February 2004

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 [CITE]). 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.