Krzysztof Nalewajko, Mitchell C. Begelman, Benoit Cerutti, Dmitri A. Uzdensky, Marek Sikora
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, D_{VHE}~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, requiring a very
high co-moving energy density in the emitting region and a very efficient
radiative process. We disfavor hadronic processes due to their low radiative
efficiency. The External Radiation Compton (ERC) mechanism involving the
infrared radiation of the dusty torus is efficient for D_{VHE}>~50. For a
magnetic field strength >~0.03 G x (D_{VHE}/20)^5, the Synchrotron Self-Compton
(SSC) process dominates the ERC. We consider a scenario involving synchrotron
emission by ultra-relativistic electrons accelerated in a magnetic reconnection
layer, as has been recently proposed for the case of HE flares in the Crab
Nebula. For the case of PKS 1222+216, this mechanism requires an effective
electric-to-magnetic field ratio within the layer of ~26 x (D_{VHE}/20)^{-1},
and a reconnecting magnetic field strength of ~130 G x (D_{VHE}/20)^{-3}. For
the origin of an extremely compact emitting region, we prefer a self-collimated
jet substructure maintaining its original energy density during propagation to
parsec scales, over global jet recollimation by the external medium.
View original:
http://arxiv.org/abs/1202.2123
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