Very-high-energy gamma-rays from the Universe's middle age: detection of
  the z=0.940 blazar PKS 1441+25 with MAGIC
  The flat-spectrum radio quasar PKS 1441+25 at a redshift of z = 0.940 is
detected between 40 and 250 GeV with a significance of 25.5 {\sigma} using the
MAGIC telescopes. Together with the gravitationally lensed blazar QSO B0218+357
(z = 0.944), PKS 1441+25 is the most distant very high energy (VHE) blazar
detected to date. The observations were triggered by an outburst in 2015 April
seen at GeV energies with the Large Area Telescope on board Fermi.
Multi-wavelength observations suggest a subdivision of the high state into two
distinct flux states. In the band covered by MAGIC, the variability time scale
is estimated to be 6.4 +/- 1.9 days. Modeling the broadband spectral energy
distribution with an external Compton model, the location of the emitting
region is understood as originating in the jet outside the broad line region
(BLR) during the period of high activity, while being partially within the BLR
during the period of low (typical) activity. The observed VHE spectrum during
the highest activity is used to probe the extragalactic background light at an
unprecedented distance scale for ground-based gamma-ray astronomy.
