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We present data for 18 blazars observed with ASCA, half of which were alsoobserved contemporaneously with EGRET as parts of multi-wavelength campaigns.The observations show a clear difference in the spectra between threesubclasses of blazars, namely the High-energy peaked BL Lac objects (HBLs),Low-energy peaked BL Lac objects (LBLs), and quasar-hosted blazars (QHBs). Wefind that the radiation process responsible for the HE peak for HBLs can beexplained solely by Synchrotron-Self-Compton (SSC) emission, with the Dopplerfactor consistent with the VLBI and/or gamma-ray variability data. For manyQHBs, on the other hand, the gamma-rays cannot be solely due to the SSCmechanism unless the Doppler factor is significantly in excess of that inferredfrom VLBI data. We consider an alternative scenario consistent with themeasured values of the Doppler factor, where the SSC component is still presentin QHBs and it dominates in the X-ray band, but it is below the observedgamma-ray spectrum. With an assumption that the peak of the SSC emission is onthe extrapolation of the X-ray spectrum, and adopting the Doppler factor of 10,we infer the magnetic field to be 0.1 - 1 Gauss, and Lorentz factors ofelectrons radiating at the peak of the nu F(nu) spectrum of 10^3 for QHBs; thisis much lower than 10^5 for HBLs. This difference is most likely due to thelarge photon density expected in QHBs.Comment: 24 pages, 4 figures, AAS Latex macro v4.0, to appear in The  Astrophysical Journa

ASCAObservations of Blazars and Multiband Analysis