The extreme flare in III Zw 2:

Evolution of a radio jet in a Seyfert galaxy

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
² Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands e-mail: brunthaler@jive.nl
³ ASTRON, Postbus 2, 7990 AA Dwingeloo, The Netherlands
⁴ Department of Astrophysics, Radboud Universiteit Nijmegen, Postbus 9010, 6500 GL Nijmegen, The Netherlands
⁵ Radio Astronomy Laboratory, University of California at Berkeley, 601 Campbell Hall, CA 94720, USA
⁶ University of Michigan, Astronomy Department, Ann Arbor, MI 48109-1090, USA
⁷ Metsähovi Radio Observatory, Helsinki University of Technology, Metsahovintie 114, 02540 Kylmälä, Finland

Received: 24 November 2004
Accepted: 24 January 2005

Abstract

A very detailed monitoring of a radio flare in the Seyfert I galaxy III Zw 2 with the VLA and the VLBA is presented. The relative astrometry in the VLBA observations was precise to a few μas. The spectral and spatial evolutions of the source are closely linked, and these observations allowed us to study a textbook example of a synchrotron self-absorbed jet in great detail. We observed a phase where the jet gets frustrated with neither expansion nor spectral evolution. Then the jet breaks free and starts to expand with apparent superluminal motion. This expansion is accompanied by a strong spectral evolution. The results are a good confirmation of synchrotron theory and equipartition for jets.