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

TL;DR

This paper proposes a magnetic reconnection minijet model to explain minute-scale TeV flares in blazars, attributing fast flares to large plasmoids formed during reconnection events at parsec-scale distances.

Contribution

It introduces a time-dependent reconnection model with plasmoid formation to explain both the day-long activity envelope and rapid flares in blazars, aligning with observed phenomena.

Findings

Reconnection layers fragment into multiple plasmoids, including large 'monster' plasmoids.

Radiation from reconnection explains the observed blazar activity envelope.

Fast TeV flares are powered by radiation from large plasmoids.

Abstract

Minute-timescale TeV flares 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>50. For TeV 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 we 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~0.3-1 pc and l' \simless 10^{16} cm, respectively. The required magnetization of the jet at this distance is modest: sigma ~a few. Such dissipation distance R_diss and reconnection size l' are expected if the jet contains field structures with size of the order of the black-hole horizon.