Multiwavelength observations of 3C 273 in 1993-1995

We present the results of the multiwavelength campaigns on 3C 273 in 1993-1995. During the observations in late 1993, this quasar showed an increase of its flux for energies greater than or equal to 100 MeV from about 2.1 x 10(-7) photons cm(-2) s(-1) to approximately 5.6 x 10(-7) photons cm(-2) s(-1) during a radio outburst at 14.5, 22, and 37 GHz. However, no one-to-one correlation of the gamma-ray radiation with any frequency could be found. The photon spectral index of the high-energy spectrum changed from Gamma(gamma) = (3.20 +/- 0.54) to Gamma(gamma) = (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 the explanation of the high gamma-ray emission of active galactic nuclei were performed to the multiwavelength spectrum of 3C 273. All three models are able to represent the basic features of the multiwavelength spectrum. Although there are some differences, the data are still not decisive enough to discriminate between the models.