Continuous Long-look Observations of TeV Blazars Using ASCA

Two uninterrupted, 10-day ASCA observations of the TeV blazars Mrk 501 and PKS 2155-304 both show continuous strong X-ray flaring. Despite the relatively faint intensity states of each source, there was no identifiable quiescent period. Structure function analysis shows both blazars have a characteristic time scale of similar to1 day, and there is little variability below that time scale. Together with symmetry of flares, we suggest the dominant time scale is the light crossing time rather than acceleration or cooling, in which case the emission region size is similar to 10(16-17) cm.