High Energy Emission from Blazars - ASCA Observation of Blazars and Multiband Analysis

We present recent observational and theoretical results for coordinated observations of BL Lac objects and OVV quasars (blazars), mainly based on ASCA observations of ~20 blazars. High Energy gamma-ray emission detected from a dozen of blazars has established that the high energy particles play an important role for the emission. The X--ray emission in blazars is radiated either via the synchrotron process by the high energy tail of the electron distribution or the Comptonization of the synchrotron photons. The observations in X-ray band and a comparison with other energy band is thus crucial to the study the emission mechanism and, specifically, the distribution of the relativistic electrons. Observation of blazar flares gives us an important opportunity to study the evolution of the spectrum during the flare. We discuss the implication of an X-ray/TeV flare from Mkn421 detected by ASCA and mention the importance of monitoring flares by the future all sky monitor.