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The $\gamma$-ray flare of PKS 1222+216, observed in June 2010, is interpretedas an outcome of jet dynamics at recollimation zone. We obtained the$\gamma$-ray light-curves in three different energy bands, namely, 100--300MeV, 300 MeV--1 GeV and 1--3 GeV from observations by the \emph{Fermi} LargeArea Telescope (LAT). We also use the \emph{Swift}--XRT flux from 0.3--10 keVobtained from archival data. We supplement these with the 0.07--0.4 TeVobservations with MAGIC telescope, available in the literature. The detectionof source at very high energy (VHE, $E>100$ GeV) with a differential photonspectral index of $2.7\pm0.3$ and the rapid variability associated with itsuggests that the emission arises from a compact region located beyond thebroad line emitting region. The plausible $\gamma$-ray emission mechanism canthen be inverse Compton scattering of IR photons from obscuring torus. Further,the decay time of LAT flare cannot be explained by considering simple radiativeloss mechanisms. Hence, to interpret the LAT light curves, we develop a modelwhere the broadband emission originates from a compact region, arisingplausibly from the compression of jet matter at the recollimation zone. Theflare is then expressed as an outcome of jet deceleration probably associatedwith this focusing effect. The parameters of the model are further constrainedby reproducing the broadband spectral energy distribution of the sourceobtained during the flare episode. Our study suggests that the particle energydensity exceeds magnetic energy density by a large factor which in turn maycause rapid expansion of the emission region. However, near equipartition canbe achieved towards the end of LAT flare during which the compact emissionregion would have expanded to the size of jet cross-section.

Gamma-ray Flare of PKS 1222+216 in 2010: Effect of Jet Dynamics at the Recollimation Zone