The blazar zone in quasars is commonly assumed to be located inside the
broad-line region at some hundreds of Schwartzschild radii from the central
black hole. Now, the simultaneous Fermi/LAT and MAGIC observations of a strong
flare in the FSRQ PKS 1222+21 (4C 21.35, z=0.432) on 2010 June 17 challenge
this picture. The spectrum can be described by a single power law with photon
index 2.72+/-0.34 between 3 GeV and 400 GeV, and this is consistent with
emission from a single component in the jet. The absence of a spectral cutoff
constrains the gamma-ray emission region to lie outside of the broad-line
region, which would otherwise absorb the VHE gamma-rays. On the other hand, the
MAGIC measurement of a doubling time of about 10 minutes indicates an extremely
compact emission region, in conflict with the "far dissipation" scenario. This
could be a hint for the importance of jet sub-structures, such as filaments,
reconnection zones or shear layers for the occurrence of blazar flares.Comment: 2011 Fermi Symposium proceedings - eConf C11050
