SIMULTANEOUS AND QUASI-SIMULTANEOUS OBSERVATIONS OF THE CONTINUUM EMISSION OF THE QUASAR-3C-273 FROM RADIO TO GAMMA-RAY ENERGIES

From June 15-28, 1991 the Compton Gamma-Ray Observatory (CGRO) observe d the radio-loud quasar 3C 273. All four CGRO instruments detected rad iation from this quasar in their relevant energy ranges (from 20 keV t o 5 GeV). Simultaneous and quasi-simultaneous observations by instrume nts sensitive at other wavelengths have also been performed. The data from all these observations, spanning the frequency range from 5 10(9) Hz to 8.5 . 10(24) Hz, were collected and analysed. Details of the ob servations and an overall energy-density spectrum are presented. This spectrum shows three maxima, one in the infrared (IR), one in the UV a nd another one at low-energy gamma-rays, the latter two having nearly the same strength of 3.1 . 10(46) erg/(s frequency decade) and 2.7 . 1 0(46) erg/(s frequency decade), respectively. At low-energy gamma-rays a break around 1 MeV (= 2.418 . 10(20) Hz) in the energy-density spec trum is evident. The change of the spectral index between X- and gamma -rays is similar to 0.8. The implications of these simultaneous and qu asi-simultaneous observations on some theoretical models are discussed .