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R. C. Hartman (NASA/GSFC), M. Boettcher (Rice University)
Of the blazars detected by EGRET in ~GeV gamma rays, 3C 279 is not only the best-observed by EGRET, but also one of the best-monitored at lower frequencies. We have assembled ten spectra, from GHz radio through GeV gamma rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data during the high state in early 1999. All of the spectra show substantial gamma-ray contribution to the total luminosity of the object; in a high state, the gamma-ray luminosity dominates over that at all other frequencies by a factor of 10 or more. There is no clear pattern of time correlation; some of the spectra are seen to cross each other, demonstrating that different wavebands do not always rise and fall together.
The spectra are modeled with combined leptonic, SSC + external Compton jet model. Spectral variability of 3C279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modelling results are consistent with the UV spectrum of 3C279 being dominated by accretion disk radiation during phases of low gamma-ray intensity.
M. Boettcher is a Chandra Fellow.