ASCA observations of blazars and multiband analysis

Abstract

We present data for 18 blazars observed with ASCA, half of which were also observed contemporaneously with EGRET as parts of multi-wavelength campaigns. the ASCA X-ray spectra of High-energy peaked BL Lacs (HBLs) are soft, and they form the highest energy tail of the low energy (synchrotron) component. The X-ray spectra of the quasar-hosted blazars (QHBs) are hard and consistent with the lowest energy end of the high energy (Compton) component. For Low-energy peaked BL Lacs (LBLs), the X-ray spectra are intermediate. We find that the radiation process responsible for the HE peak for HBLs can be explained solely by Synchrotron-Self-Compton (SSC) emission. For many QHBs, on the other hand, the γ-rays cannot be solely due to the SSC mechanism. We consider an alternative scenario for QHBs where the SSC component dominates in the X-ray band, but it is below the observed γ-ray spectrum. We infer the magnetic field B to be 0.1 – 1 Gauss, and Lorentz factors γ b of electrons radiating at the peak of the ν F(ν) spectrum of ∼ 10 3 for QHBs. This is much lower than γ b ∼ 10 5 for HBLs.