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Search for Very-High-Energy Gamma Rays from the z = 0.896 Quasar 4C +55.17 with the MAGIC telescopes

The bright gamma-ray quasar 4C +55.17 is a distant source (z=0.896) with a hard spectrum at GeV energies as observed by the Large Area Telescope (LAT) on board the Fermi satellite. This source is identified as a good source candidate for very-high-energy (VHE ; >30 GeV) gamma rays. In general VHE gamma rays from distant sources provide an unique opportunity to study the extragalactic background light (EBL) and underlying astrophysics. The flux intensity of this source in the VHE range is investigated. Then, constraints on the EBL are derived from the attenuation of gamma-ray photons coming from the distant blazar. We searched for a gamma-ray signal from this object using the 35-hour observations taken by the MAGIC telescopes between November 2010 and January 2011. No significant VHE gamma-ray signal was detected. We computed the upper limits of the integrated gamma-ray flux at 95% confidence level of 9.4 x 10^(−12) cm^(−2) s^(−1) and 2.5 x 10^(−12) cm^(−2) s^(−1) above 100 GeV and 200 GeV, respectively. The differential upper limits in four energy bins in the range from 80 GeV to 500 GeV are also derived. The upper limits are consistent with the attenuation predicted by low-flux EBL models on the assumption of a simple power-law spectrum extrapolated from LAT data.

galaxies: active; galaxies: nuclei; quasars: individual: 4C +55.17; gamma-rays: galaxies; radiation mechanisms: non-thermal

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