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Very High Energy (VHE) gamma-ray emission from the flat spectrum radio quasar(FSRQ) PKS 1222+21 (4C 21.35, z=0.432) was detected with the MAGIC Cherenkovtelescopes during a short observation (~0.5 hr) performed on 2010 June 17. TheMAGIC detection coincides with high energy MeV/GeV gamma-ray activity measuredby the Large Area Telescope (LAT) on board the Fermi satellite. The VHEspectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV andcan be well described by a power law dN/dE \propto E^-Gamma with a photon indexGamma= 3.75+/-0.27stat +/-0.2syst. The averaged integral flux above 100 GeV is(4.56+/-0.46)x10^(-10) cm^-2 s^-1 (~1 Crab Nebula flux). The VHE flux measuredby MAGIC varies significantly within the 30 min exposure implying a fluxdoubling time of about 10 min. The VHE and MeV/GeV spectra, corrected for theabsorption by the extragalactic background light (EBL), can be described by asingle power law with photon index 2.72+/-0.34 between 3 GeV and 400 GeV, andis consistent with emission belonging to a single component in the jet. Theabsence of a spectral cutoff constrains the gamma-ray emission region outsidethe Broad Line Region, which would otherwise absorb the VHE gamma-rays.Together with the detected fast variability, this challenges present emissionmodels from jets in FSRQ. Moreover, the combined Fermi/LAT and MAGIC spectraldata yield constraints on the density of the Extragalactic Background Light inthe UV-optical to near-infrared range that are compatible with recent models.

MAGIC discovery of VHE Emission from the FSRQ PKS 1222+21