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 {{\it 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
$9.4 \times 10^{-12}$ cm$^{-2}$ s$^{-1}$ and $2.5 \times 10^{-12}$ 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.
