Abstract

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