Letter to the Editor

A historic jet-emission minimum reveals hidden spectral features in 3C 273

¹ INTEGRAL Science Data Centre, Ch. d'Ecogia 16, 1290 Versoix, Switzerland e-mail: Marc.Turler@obs.unige.ch
² Geneva Observatory, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, casilla 19 001, Santiago, Chile
⁴ University of Michigan, Department of Astronomy, 817 Dennison Building, Ann Arbor MI, 48 109 USA
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53 121 Bonn, Germany
⁶ Metsähovi Radio Observatory, Helsinki University of Technology, Metsähovintie, 02 540 Kylmälä, Finland
⁷ Institute for Astrophysical Research, Boston Univ., 725 Commonwealth Ave., Boston MA, 02 215, USA
⁸ School of Physics and Astronomy, The University, Southampton SO17 1BJ, UK
⁹ Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
¹⁰ UK Astronomy Technology Centre, Royal Observatory Edinburgh, EH9 3HJ, UK
¹¹ Institut de Radio Astronomie Millimétrique (IRAM), Avd. Div. Pastora 7NC, 18 012 Granada, Spain

Received: 9 December 2005
Accepted: 20 March 2006

Abstract

Aims. The aim of this work is to identify and study spectral features in the quasar 3C 273 usually blended by its strong jet emission.

Methods. A historic minimum in the sub-millimetre emission of 3C 273 triggered coordinated multi-wavelength observations in June 2004. X-ray observations from the INTEGRAL, XMM-Newton and RXTE satellites are complemented by ground-based optical, infrared, millimetre and radio observations. The overall spectrum is used to model the infrared and X-ray spectral components.

Results. Three thermal dust emission components are identified in the infrared. The dust emission on scales from 1 pc to several kpc is comparable to that of other quasars, as expected by AGN unification schemes. The observed weakness of the X-ray emission supports the hypothesis of a synchrotron self-Compton origin for the jet component. There is a clear soft-excess and we find evidence for a very broad iron line which could be emitted in a disk around a Kerr black hole. Other signatures of a Seyfert-like X-ray component are not detected.

Conclusions.