Broadband spectral analysis of PKS 0528+134:: A report on six years of Egret observations

The multiwavelength spectra of PKS 0528 + 134 during 6 yr of observations by EGRET have been analyzed using synchrotron self-Compton (SSC) and external radiation Compton (ERC) models. We find that a two-component model, in which the target photons are produced externally to the gamma-ray-emitting region, but also including an SSC component, is required to reproduce suitably the spectral energy distributions of the source. Our analysis indicates that there is a trend in the observed properties of PKS 0528 + 134, as the source goes from a gamma-ray low state to a flaring state. We observe that during the higher gamma-ray states, the bulk Lorentz factor of the jet increases and the ERC component dominates the high-energy emission. Our model calculations indicate the trend that the energies of the electrons giving rise to the synchrotron peak decrease, and the power-ratio of the gamma-ray and low-energy spectral components increases, as the source goes from a low to a high gamma-ray state.