Multiwavelength Observations of 3C 273 in 1993–1995

We present the results of the multi-wavelength campaigns on 3C 273 in1993-1995. During the observations in late 1993 this quasar showed an increaseof its flux for energies greater equal 100 MeV from about 2.1 x 10^-7photons/cm^2/s to approximately 5.6 x 10^-7 photons/cm^2/s during a radiooutburst at 14.5, 22 and 37 GHz. However, no one-to-one correlation of thegamma-ray radiation with any frequency could be found. The photon spectralindex of the high energy spectrum changed from (3.20 +- 0.54) to (2.20 +- 0.22)in the sense that the spectrum flattened when the gamma-ray flux increased.Fits of the three most prominent models (synchrotron self-Comptonization,external inverse Comptonization and the proton initiated cascade model) for theexplanation of the high gamma-ray emission of active galactic nuclei wereperformed to the multi-wavelength spectrum of 3C 273. All three models are ableto represent the basic features of the multi-wavelength spectrum. Althoughthere are some differences the data are still not decisive enough todiscriminate between the models.Comment: 63 pages including 9 eps figures and 9 tables, LateX, uses aaspp4.sty and tighten.sty, accepted for publication in Ap