1995A&A...298..711L

From June 15-28, 1991 the Compton Gamma-Ray Observatory (CGRO) observed the radio-loud quasar 3C 273. All four CGRO instruments detected radiation from this quasar in their relevant energy ranges (from 20keV to 5GeV). Simultaneous and quasi-simultaneous observations by instruments sensitive at other wavelengths have also been performed. The data from all these observations, spanning the frequency range from 5.10⁹Hz to 8.5.10²⁴Hz, were collected and analysed. Details of the observations and an overall energy-density spectrum are presented. This spectrum shows three maxima, one in the infrared (IR), one in the UV and another one at low-energy γ-rays, the latter two having nearly the same strength of 3.1.10⁴⁶erg/(s frequency decade) and 2.7.10⁴⁶erg/(s frequency decade), respectively. At low-energy γ-rays a break around 1MeV (=2.418.10²⁰Hz) in the energy-density spectrum is evident. The change of the spectral index between X- and γ-rays is ∼0.8. The implications of these simultaneous and quasi-simultaneous observations on some theoretical models are discussed.