  We study several properties of blazars detected in the gamma-ray energy range
by comparing the EGRET sources with a sample of radio blazars which can be
considered possible gamma-ray candidates. We define three classes:
non-gamma-ray blazars, blazars with quasi-steady gamma-ray emission, and
gamma-ray blazars with substantial activity level. By combining the information
of detected and candidate AGNs, we characterise the blazar activity, including
the discovery of a region of consistency between the gamma-ray flaring
duty-cycle and the recurrence time between flares. We also find a possible
relation between the activity index of FSRQs and their black hole mass.

Astrophysics