We study theoretical implications of a rapid Very-High-Energy ( VHE ) flare detected by MAGIC in the Flat-Spectrum Radio Quasar PKS 1222+216 .
The minimum distance from the jet origin at which this flare could be produced is 0.5 { pc } .
A moderate Doppler factor of the VHE source , \mathcal { D } _ { VHE } \sim 20 , is allowed by all opacity constraints .
The concurrent High-Energy ( HE ) emission observed by Fermi provides estimates of the total jet power and the jet magnetic field strength .
Energetic constraints for the VHE flare are extremely tight : for an isotropic particle distribution they require a huge co-moving energy density in the emitting region and a very efficient radiative process .
We disfavor hadronic processes due to their low radiative efficiency , as well as the synchrotron scenario recently proposed for the case of HE flares in the Crab Nebula , since the parameters needed to overcome the radiative losses are quite extreme .
The VHE emission can be explained by the Synchrotron Self-Compton ( SSC ) mechanism for \mathcal { D } _ { VHE } \sim 20 or by the External Radiation Compton ( ERC ) mechanism involving the infrared radiation of the dusty torus for \mathcal { D } _ { VHE } \sim 50 .
After discussing several alternative scenarios , we propose that the extreme energy density constraint can be satisfied when the emission comes from highly anisotropic short-lived bunches of particles formed by the kinetic beaming mechanism in magnetic reconnection sites .
By focusing the emitting particles into very narrow beams , this mechanism allows one to relax the causality constraint on the source size , decreasing the required energy density by 4 orders of magnitude .