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Observational evidence for the accretion-disk origin for a radio jet in an active galaxy


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 Galaxy1,2,3. 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.

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Figure 1: Sequence of VLBA images of 3C120 at a frequency of 43 GHz.
Figure 2: Time dependence of the X-ray and radio emission of 3C120.

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We gratefully acknowledge partial support for this research from the US National Science Foundation (NSF), NASA, the Fulbright Commission for collaboration between Spain and the USA, and the Spanish Dirección General de Investigación Científica Técnica. The VLBA is an instrument of the National Radio Astronomy Observatory, a facility of the NSF operated under cooperative agreement by Associated Universities Inc. The University of Michigan Radio Astronomy Observatory was funded in part by the NSF and by the University of Michigan Department of Astronomy.

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Correspondence to Alan P. Marscher.

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Marscher, A., Jorstad, S., Gómez, JL. et al. Observational evidence for the accretion-disk origin for a radio jet in an active galaxy. Nature 417, 625–627 (2002).

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