Gamma rays from the quasar PKS 1441+25: story of an escape
  Outbursts from gamma-ray quasars provide insights on the relativistic jets of
active galactic nuclei and constraints on the diffuse radiation fields that
fill the Universe. The detection of significant emission above 100 GeV from a
distant quasar would show that some of the radiated gamma rays escape
pair-production interactions with low-energy photons, be it the extragalactic
background light (EBL), or the radiation near the supermassive black hole lying
at the jet's base. VERITAS detected gamma-ray emission up to 200 GeV from PKS
1441+25 (z=0.939) during April 2015, a period of high activity across all
wavelengths. This observation of PKS 1441+25 suggests that the emission region
is located thousands of Schwarzschild radii away from the black hole. The
gamma-ray detection also sets a stringent upper limit on the near-ultraviolet
to near-infrared EBL intensity, suggesting that galaxy surveys have resolved
most, if not all, of the sources of the EBL at these wavelengths.
