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We studied the rapid variability at GeV gamma rays of the flat-spectrum radioquasar PKS 1222+216, which was recently found by the MAGIC Cerenkov telescopeto display very short variability (minutes time scale) at hundreds of GeV. Weanalyzed the time period between 2010 April 29 and June 20, when the sourcegenerated a few gamma-ray flares with flux in the MeV-GeV band in excess of10^-5 ph cm^-2 s^-1 on daily basis. We set tight upper limits on the observeddoubling time scale (about 1 hour on 2010 April 30), the smallest measured todate at MeV-GeV energies, which can constrain the size of the gamma-rayemitting region. We also studied the spectra measured during two flares (2010April 30 and June 17-18). The combination of spectral and variability studiesobtained in the present work favors the hypothesis that gamma rays aregenerally produced inside the broad-line region (BLR), but sometimes thedissipation can occur at larger distances, nearby the infrared torus.

Short time scale variability at gamma rays in FSRQs and implications on the current models