The 1993 multiwavelength campaign on 3C 279: The radio to gamma-ray energy distribution in low state

Simultaneous observations of 3C 279 at radio, millimeter, near-infrared, optical, ultraviolet (with IUE) and X-ray (with ROSAT) wavelengths were obtained in 1992 December-1993 January, during a three week pointing at the source by the Compton Gamma Ray Observatory. The blazar was in a quiescent or "low" state during this period. Comparing the multiwavelenth energy distribution to that from 1991 June, when 3C 279 was in its brightest recorded γ-ray state, we find the following: 1. 3C 279 faded dramatically at all frequencies above 1014 Hz, while the flux variations at low frequencies (radio to millimeter wavelengths) were minor. 2. The near-infrared-optical-ultraviolet spectral shape was softer (steeper) in the quiescent state, and the X-ray spectra also appear softer, although the spectral indix measured by ROSAT refer to a lower energy band than that measured earlier with Ginga. 3. The ratio of the γ-ray luminosity to that across all other frequencies decreased from a value of ≃10 in the flaring state to a value ≃1 in the quiescent state. These findings imply that the production of γ-rays is closely related to the optical-ultraviolet continuum, in agreement with models where γ-rays are produced through inverse Compton (IC) scattering by relativistic electrons emitting the synchrotron continuum. The observed nonlinear relation between the synchrotron and IC requires both a change in the electron spectrum and an associated change in the seed photons.