9 Conclusion  

This paper is the witness of the enormous observing effort made all over the world to monitor 3C 273 at every possible wavelength during more than 30 years. It is to the best of our knowledge the first attempt of making an archive grouping together most available observations of a single AGN through the entire electro-magnetic spectrum. Such a database, apart from making data publicly available, ensures that early observations sometimes only published in graphical form are not completely lost after a few decades.

The aim of the database presented here is to make the analysis of multi-wavelength variability possible for a large community of astronomers. We are convinced that such studies are of great help to the understanding of the physical processes at work in 3C 273. This paper might also stimulate the creation of similar archives for other well observed AGN (Seyfert galaxies or blazars), which would enable the direct comparison of variability between different object classes and hence constrain the unification models of AGN.

Acknowledgements

We are very grateful to all observers and collaborators, who participated in the Geneva photometric monitoring of 3C 273. We also thank D.C. Backer and R. Barvainis for providing us the 89GHz observations from Hat Creek and the 87GHz FCRAO observations, respectively. M. Aller and H. Aller would like to acknowledge partial support by the National Science Foundation (NSF) from grant AST 94-21979 and preceding grants. The BIMA array is operated by the Berkeley-Illinois-Maryland Association under funding from the NSF under grant AST 93-20238. The GBI was operated by the National Radio Astronomy Observatory under contract to the US Naval Observatory and the Naval Research Laboratory (NRL) during the time period of these observations. Radio astronomy at the NRL is supported by the Office of Naval Research.