MAGIC discovery of very high energy emission from the FSRQ PKS 1222+21

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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 Cherenkov telescopes during a short observation (similar to 0.5 hr) 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 proportional to E-Gamma with a photon index Gamma = 3.75 +/- 0.27(stat) +/- 0.2(syst). The averaged integral flux above 100 GeV is (4.6 +/- 0.5) x 10(-10) cm(-2) s(-1) (similar to 1 Crab Nebula flux). The VHE flux measured by MAGIC varies significantly within the 30 minute exposure implying a flux doubling time of about 10 minutes. The VHE and MeV/GeV spectra, corrected for the absorption by the extragalactic background light (EBL), can be described by a single power law with photon index 2.72 +/- 0.34 between 3 GeV and 400 GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the gamma-ray emission region to lie 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 FSRQs. Moreover, the combined Fermi/LAT and MAGIC spectral data yield constraints on the density of the EBL in the UV-optical to near-infrared range that are compatible with recent models.
© The American Astronomical Society. Supported by INFN Padova.We thank the Instituto de Astrofisica de Canarias for the excellent working conditions at the Observatorio del Roque de los Muchachos in La Palma. The support of the German BMBF and MPG, the Italian INFN, the Swiss National Fund SNF, and the Spanish MICINN is gratefully acknowledged. This work was also supported by the Marie Curie program, by the CPAN CSD2007-00042 and MultiDark CSD2009-00064 projects of the Spanish Consolider-Ingenio 2010 programme, by grant DO02-353 of the Bulgarian NSF, by grant 127740 of the Academy of Finland, by the YIP of the Helmholtz Gemeinschaft, by the DFG Cluster of Excellence "Origin and Structure of the Universe," and by the Polish MNiSzW Grant N N203 390834.The Fermi/LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged.
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