The \gamma -ray flare of PKS 1222+216 , observed in June 2010 , is interpreted as an outcome of jet dynamics at recollimation zone .
We obtained the \gamma -ray light-curves in three different energy bands , namely , 100–300 MeV , 300 MeV–1 GeV and 1–3 GeV from observations by the Fermi Large Area Telescope ( LAT ) .
We also use the Swift –XRT flux from 0.3–10 keV obtained from archival data .
We supplement these with the 0.07–0.4 TeV observations with MAGIC telescope , available in the literature .
The detection of source at very high energy ( VHE , E > 100 GeV ) with a differential photon spectral index of 2.7 \pm 0.3 and the rapid variability associated with it suggests that the emission arises from a compact region located beyond the broad line emitting region .
The plausible \gamma -ray emission mechanism can then be inverse Compton scattering of IR photons from obscuring torus .
Further , the decay time of LAT flare can not be explained by considering simple radiative loss mechanisms .
Hence , to interpret the LAT light curves , we develop a model where the broadband emission originates from a compact region , arising plausibly from the compression of jet matter at the recollimation zone .
The flare is then expressed as an outcome of jet deceleration probably associated with this focusing effect .
Based on this model , the rise of the LAT flare is attributed to the opening of emission cone followed by the decay resulting from jet deceleration .
The parameters of the model are further constrained by reproducing the broadband spectral energy distribution of the source obtained during the flare episode .
Our study suggests that the particle energy density exceeds magnetic energy density by a large factor which in turn may cause rapid expansion of the emission region .
However , near equipartition can be achieved towards the end of LAT flare during which the compact emission region would have expanded to the size of jet cross-section .