The multiwavelength variability of 3C 273

¹ ISDC Data Centre for Astrophysics, Chemin d'Écogia 16, 1290 Versoix, Switzerland e-mail: Simona.Soldi@obs.unige.ch
² Observatoire de Genève, University of Geneva, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
³ University of Michigan, Department of Astronomy, 817 Dennison Building, Ann Arbor, MI 48 109, USA
⁴ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁵ Metsähovi Radio Observatory, Helsinki University of Technology, TKK, Metsähovintie 114, 02540 Kylmälä, Finland
⁶ School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁷ UK Astronomy Technology Centre, Royal Observatory Edinburgh, EH9 3HJ, UK
⁸ IAAT, Abt. Astronomie, Universität Tübingen, Sand 1, 72076 Tübingen, Germany

Received: 11 April 2008
Accepted: 16 May 2008

Abstract

Aims. We present an update of the 3C 273's database hosted by the ISDC, completed with data from radio to gamma-ray observations over the last 10 years. We use this large data set to study the multiwavelength properties of this quasar, especially focussing on its variability behaviour.

Methods. We study the amplitude of the variations and the maximum variability time scales across the broad-band spectrum and correlate the light curves in different bands, specifically with the X-rays, to search for possible connections between the emission at different energies.

Results. 3C 273 shows variability at all frequencies, with amplitudes and time scales strongly depending on the energy and being the signatures of the different emission mechanisms. The variability properties of the X-ray band imply the presence of either two separate components (possibly a Seyfert-like and a blazar-like) or at least two parameters with distinct timing properties to account for the X-ray emission below and above ~20 keV. The dominant hard X-ray emission is most probably not due to electrons accelerated by the shock waves in the jet as their variability does not correlate with the flaring millimeter emission, but seems to be associated to long-timescale variations in the optical. This optical component is consistent with being optically thin synchrotron radiation from the base of the jet and the hard X-rays would be produced through inverse Compton processes (SSC and/or EC) by the same electron population. We show evidence that this synchrotron component extends from the optical to the near-infrared domain, where it is blended by emission of heated dust that we find to be located within about 1 light-year from the ultraviolet source.