tokens: We thank the authors of K16 , especially M. Kadler and F. Krauss for providing the data on PKS B1424-418. S.G. and M.P. acknowledge support by the Helmholtz Alliance for Astroparticle Physics (HAP) funded by the Initiative and Networking Fund of the Helmholtz Association. W.W. acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant No. 646623).
ner_tags: O O O O O B-Citation O O B-Person I-Person O B-Person I-Person O O O O O B-CelestialObject I-CelestialObject B-Person O B-Person O O O O B-Organization I-Organization I-Organization I-Organization I-Organization B-Organization O O O B-Grant I-Grant I-Grant I-Grant O O B-Organization I-Organization B-Person O O O O B-Organization I-Organization I-Organization B-Organization O O B-Location I-Location B-Grant I-Grant I-Grant I-Grant I-Grant I-Grant B-Grant I-Grant I-Grant