Reconnection-driven plasmoids in blazars: fast flares on a slow envelope

TeV flares of a duration of similar to 10 min have been observed in several blazars. The fast flaring requires compact regions in the jet that boost their emission towards the observer at an extreme Doppler factor of delta(em) greater than or similar to 50. For similar to 100 GeV photons to avoid annihilation in the broad-line region of PKS 1222+216, the flares must come from large (pc) scales, challenging most models proposed to explain them. Here I elaborate on the magnetic reconnection minijet model for the blazar flaring, focusing on the inherently time-dependent aspects of the process of magnetic reconnection. I argue that, for the physical conditions prevailing in blazar jets, the reconnection layer fragments, leading to the formation a large number of plasmoids. Occasionally, a plasmoid grows to become a large, 'monster' plasmoid. I show that radiation emitted from the reconnection event can account for the observed 'envelope' of day-long blazar activity, while radiation from monster plasmoids can power the fastest TeV flares. The model is applied to several blazars with observed fast flaring. The inferred distance of the dissipation zone from the black hole and the typical size of the reconnection regions are R-diss similar to 0.3-1 pc and l' less than or similar to 10(16) cm, respectively. The required magnetization of the jet at this distance is modest: sigma similar to a few. Such distance R-diss and reconnection size l' are expected if the jet contains field structures with a size of the order of the black hole horizon.