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

Very High Energy (VHE) gamma-ray emission from the flat spectrum radio quasar PKS 1222+21 (4C 21.35, z=0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (~0.5 h) performed on 2010 June 17. The MAGIC detection coincides with high energy MeV/GeV gamma-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The VHE spectrum measured by MAGIC extends from about 70 GeV up to at least 400 GeV and can be well described by a power law dN/dE e^(-G) with a photon index G = 3.75+/-0.27stat +/-0.2syst. The averaged integral flux above 100 GeV is (4.56+/-0.46) 10^(-10) cm^(-2 )s^(-1). The VHE flux measured by MAGIC varies significantly within the 30 min exposure implying a flux doubling time of about 10 min. The absence of a spectral cutoff constrains the gamma-ray emission region outside the Broad Line Region, which would otherwise absorb the VHE gamma- rays. Together with the detected fast variability, this challenges present emission models from jets in flat spectrum radio quasars. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the Extragalactic Background Light in the UV-optical to near-infrared range that are compatible with recent models.

galaxies: active; galaxies: jets; BL Lacertae objects: individual (PKS 1222+21); cosmic background radiation; gamma rays: galaxies

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