The origin of intrinsic variability of intraday variable sources

¹ Institut d'Astrophysique, 98bis Bd Arago, 75014 Paris, France e-mail: roland@iap.fr
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn 53121, Germany

Received: 30 July 2008
Accepted: 4 December 2008

Abstract

Intraday variability (IDV) describes flux-density variations in the radio regime on timescales of a day and less. The origin of such variations has been attributed to both source intrinsic and extrinsic mechanisms. While there is growing evidence that faster flux- density variations (on the order of hours to minutes) are caused by refractive interstellar scattering, extrinsic mechanisms alone still fail to explain all the observations. In particular, in the blazar S5 0716+714, correlated variations at frequencies in the radio and the optical regimes indicate an intrinsic component to the variability. Using the characteristics of the relativistic ejection found for the blazar S5 1803+784, we find that the formation and the rotation of a warp in the inner part of the accretion disk produce a small perturbation of the relativistic beam and consequently a variation in the viewing angle and in the beamed synchrotron emission. We find that the relative flux variations become chaotic if the amplitude of the perturbation exceeds a critical value. We investigate the properties of the chaotic behavior of the solution to explain the observed properties of IDV sources, such as the flux variations, the polarized flux variations, and the observable frequency dependence. As a warp can form naturally in the inner part of the accretion disk, we conclude that both intrinsic and extrinsic mechanisms produce IDV sources.