Constraints given by the MAGIC discovery of the Flat Spectrum Radio Quasar PKS1222+21 in VHE Gamma rays

• Published in: Journal of physics. Conference series Vol. 355; no. 1; p. 12018
• Main Authors: Becerra-González, J, Stamerra, A, Saito, K, Mazin, D, Tavecchio, F, Maraschi, L, Terzic, T, Prandini, E, Sitarek, J
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 26.03.2012
• Subjects: Crab nebula; Diameters; Gamma emission; Gamma ray astronomy; Gamma ray sources; Gamma ray telescopes; Gamma rays; Physics; Quasars; Red shift; Telescopes
• ISSN: 1742-6596; 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/355/1/012018

The MAGIC telescopes discovered very high energy (VHE, E>100 GeV) gamma-ray emission coming from the distant Flat Spectrum Radio Quasar (FSRQ) PKS 1222+21 (4C +21.35, z 0.432). It is the second most distant VHE gamma-ray source, with well measured redshift, detected until now. The observation was performed on 2010 June 17 (MJD 55364.9) using the two 17 m diameter imaging Cherenkov telescopes on La Palma (Canary Islands, Spain). 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 averaged integral flux above 100 GeV is equivalent to 1 Crab Nebula flux. The VHE flux measured by MAGIC varies significantly within the 30 minutes of 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, can be described by a single power law with photon index 2.72±0.34 between 3 GeV and 400 GeV, consistent with gamma-ray emission belonging to a single component in the jet. The absence of a spectral cut-off 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.