Magic discovery of very high energy emission from the FSRQ PKS1222+21

Abstract

Very high energy (VHE) γ-ray emission from the flat spectrum radio quasar (FSRQ) PKS1222+21 (4C21.35, z = 0.432) was detected with the MAGIC Cherenkov telescopes during a short observation (0.5hr) performed on 2010 June 17. 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 VHE spectrum measured by MAGIC extends from about 70GeV up to at least 400GeV and can be well described by a power-law dN/dE E -Γ with a photon index Γ = 3.75 0.27stat 0.2syst. The averaged integral flux above 100GeV is (4.6 0.5) × 10-10 cm-2 s-1 (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 3GeV and 400GeV, and is consistent with emission belonging to a single component in the jet. The absence of a spectral cutoff constrains the γ-ray emission region to lie outside the broad-line region, which would otherwise absorb the VHE γ-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. © 2011. The American Astronomical Society. All rights reserved.