MULTIWAVELENGTH OBSERVATIONS OF 3C-273 IN 1993-1995

We present the results of the multiwavelength campaigns on 3C 273 in 1 993-1995. During the observations in late 1993, this quasar showed an increase of its flux for energies greater than or equal to 100 MeV fro m 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 a ny frequency could be found. The photon spectral index of the high-ene rgy spectrum changed from Gamma(gamma) = (3.20 +/- 0.54) to Gamma(gamm a) = (2.20 +/- 0.22) in the sense that the spectrum flattened when the gamma-ray flux increased. Fits of the three most prominent models (sy nchrotron self-Comptonization, external inverse Comptonization, and th e proton-initiated cascade model) for the explanation of the high gamm a-ray emission of active galactic nuclei were performed to the multiwa velength spectrum of 3C 273. All three models are able to represent th e basic features of the multiwavelength spectrum. Although there are s ome differences, the data are still not decisive enough to discriminat e between the models.