MAGIC discovery of the distant quasar 4C +21.35 in VHE gamma rays

Abstract

The MAGIC telescopes discovered Very High Energy (VHE, E>100 GeV) γ-ray emission coming from the distant Flat Spectrum Radio Quasar (FSRQ) 4C +21.35 (PKS 1222+21, z=0.432) [1, 2]. 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 γ-ray activity measured by the Large Area Telescope (LAT) on board the Fermi satellite. The averaged integral flux above 100 GeV measured by MAGIC is(4.6� 0.5)� 10 −10 cm −2 s −1 (� 1 Crab Nebula flux). The MAGIC measured spectrum can be well described by a simple power law from 70 GeV to at least 400 GeV. The combined VHE and MeV/GeV spectrum corrected for the absorption by the extragalactic background light is consistent with a simple power law from 3 GeV up to 400 GeV, suggesting that the emission is coming from the same single component in the jet. The absence of a spectral cutoff indicates that the γ-ray emission region is outside of the Broad Line Region. We also detected fast variability in VHE γ-rays with a flux doubling time of 8 .6 +1.1 −0.9 minutes. This fast variability together with the spectral signatures are very challenging for the present je t emission models of FSRQs.