1. Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, Massachusetts 02215, USA
2. Sobolev Astronomical Institute, St Petersburg State University, Universitetskii Prospekt 28, Petrodvorets, St Petersburg, 198504, Russia
3. Insituto de Astrofísica de Andalucía (CSIC), Apartado Correos 3004, Granada, E-18080, Spain
4. Astronomy Department, University of Michigan, 830 Dennison, 501 East University Street, Ann Arbor, Michigan 48109-1090, USA
5. Metsähovi Radio Observatory, Helsinki University of Technology, Metsähovintie 114, Kylmala, Finland-02540
6. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, Virginia 22903-2475, USA
7. Center for Astrophysics, University of Central Lancashire, Preston, Lancashire, PR1 2HE, UK

Correspondence to: Alan P. Marscher¹ Correspondence and requests for materials should be addressed to A.P.M. (e-mail: Email: marscher@bu.edu).

Abstract

Accretion of gas onto black holes is thought to power the relativistic jets of material ejected from active galactic nuclei (AGN) and the 'microquasars' located in our Galaxy^{1, 2, 3}. In microquasars, superluminal radio-emitting features appear and propagate along the jet shortly after sudden decreases in the X-ray fluxes¹. This establishes a direct observational link between the black hole and the jet: the X-ray dip is probably caused by the disappearance of a section of the inner accretion disk⁴ as it falls past the event horizon, while the remainder of the disk section is ejected into the jet, creating the appearance of a superluminal bright spot⁵. No such connection has hitherto been established for AGN, because of insufficient multi-frequency data. Here we report the results of three years of monitoring the X-ray and radio emission of the galaxy 3C120. As has been observed for microquasars, we find that dips in the X-ray emission are followed by ejections of bright superluminal knots in the radio jet. The mean time between X-ray dips appears to scale roughly with the mass of the black hole, although there are at present only a few data points.