X-Ray Variability of Blazars

This thesis is dealing with the X-ray variability characteristics of blazars, using data obtained mostly with BeppoSAX. First we performed a comprehensive variability analysis on two TeV sources, MKN 421 and PKS 2155-304, respectively. We then studied possible variability trend in the blazars class as a whole. MKN 421 and PKS 2155-304, monitored with BeppoSAX between 1996 and 2000, showed very similar variability characteristics. The light curves are characterized by recurrent flares with durations of ~ 1 day. The quasi-symmetric structure of the flares is seen in most cases. In general, the variability amplitude is larger and time scale shorter with increasing energy, but do not correlate with the luminosity. The structure functions are characterized by a steep slope of ~ 1.2 at short time scales, with a clear turn-over at a characteristic time scale of ~ 0.5 days. A probable flare periodicity of ~ 1 day was present in the 2000 observations of MKN 421. Soft lags, hard lags, and zero lags between different X-ray energies were detected in MI