Broadband Spectral Analysis of PKS 0528+134: A Report on Six Years of EGRET Observations

The multiwavelength spectra of PKS 0528+134 during six years of observationsby EGRET have been analyzed using synchrotron self-Compton (SSC) and externalradiation Compton (ERC) models. We find that a two-component model, in whichthe target photons are produced externally to the gamma-ray emitting region,but also including an SSC component, is required to suitably reproduce thespectral energy distributions of the source. Our analysis indicates that thereis a trend in the observed properties of PKS 0528+134, as the source goes froma gamma-ray low state to a flaring state. We observe that during the highergamma-ray states, the bulk Lorentz factor of the jet increases and the ERCcomponent dominates the high-energy emission. Our model calculations indicatethe trend that the energies of the electrons giving rise to the synchrotronpeak decreases, and the power-ratio of the gamma-ray and low energy spectralcomponents increases, as the source goes from a low to a high gamma-ray state.Comment: 36 pages, 13 figures, final version accepted for publication in ApJ; includes minor modification