Coordinated Multiwavelength Observations and Spectral Variability Modeling of Gamma-Ray Blazars

Our recent progress on time-dependent modeling of the multiwavelength spectra and variability of blazars with leptonic and hadronic jet models is reviewed. Special emphasis is placed on X-ray spectral variability of low-frequency peaked (LBLs) and intermediate BL Lac objects (IBLs). As an example, recent observational and modeling results of an extensive multiwavelength campaign of BL Lacertae in 2000 are presented. It is demonstrated how combined spectral and variability modeling of LBLs and IBLs can significantly constrain emission models and potential variability scenarios. In the case of BL Lacertae, the variability appears to be driven primarily by fluctuations in the spectral index of the non-thermal, ultrarelativistic electron population in the jet. Such constraints allow us to refine predictions of the intrinsic GeV gamma-ray emission and the dominant electron cooling mechanism in these objects.