1996A&AS..120C.537M

Observations of multiwaveband spectra and variability of γ-ray bright blazars are related to the synchrotron self-Compton (SSC) emission model. Models involving radiation from a relativistic jet can fit the June 1991 multiwaveband spectrum of 3C 279. Optical flares that are simultaneous with, or lag by about one day, γ-ray flares are easily explained by the SSC model. Optical variations that precede those in the γ-ray, however, require that the optically emitting region be distinct from, and closer to the central engine than, the γ-ray/infrared region. The proximity of the γ-ray and optical/infrared emission sites in 3C 279, combined with the need for strong Doppler boosting in the γ-ray, implies that the optical/infrared radiation is also strongly beamed, contrary to some jet models. Models in which the γ-rays are up-scattered seed photons from outside the jet can explain the flares only if the variations are caused by rapid changes in Doppler factor. For the TeV γ-ray source Mkn 421, the May 1994 flare at TeV and keV energies was not seen at GeV or eV energies. This appears to correspond to an increase in the upper-energy cutoff to the relativistic electron energy distribution without a change in the normalization or slope.