skip to main content

Title: VERY HIGH ENERGY γ-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 25.5σ 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 timescale 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.
Authors:
;  [1] ; ;  [2] ; ; ;  [3] ;  [4] ;  [5] ;  [6] ; ; ;  [7] ; ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] more »; ; ; « less
  1. ETH Zurich, CH-8093 Zurich (Switzerland)
  2. Università di Udine, and INFN Trieste, I-33100 Udine (Italy)
  3. INAF National Institute for Astrophysics, I-00136 Rome (Italy)
  4. Università di Siena, and INFN Pisa, I-53100 Siena (Italy)
  5. Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka, University of Split and University of Zagreb (Croatia)
  6. Saha Institute of Nuclear Physics, 1\AF Bidhannagar, Salt Lake, Sector-1, Kolkata 700064 (India)
  7. Max-Planck-Institut für Physik, D-80805 München (Germany)
  8. Universidad Complutense, E-28040 Madrid (Spain)
  9. University of Łódź, PL-90236 Lodz (Poland)
  10. Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen (Germany)
  11. IFAE, Campus UAB, E-08193 Bellaterra (Spain)
  12. Universität Würzburg, D-97074 Würzburg (Germany)
  13. Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, E-28040 Madrid (Spain)
Publication Date:
OSTI Identifier:
22518655
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 815; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BACKGROUND RADIATION; DETECTION; DISTANCE; ENERGY SPECTRA; GALAXIES; GAMMA ASTRONOMY; GAMMA RADIATION; GEV RANGE; GRAVITATIONAL LENSES; JETS; PROBES; QUASARS; RED SHIFT; TELESCOPES; UNIVERSE; VISIBLE RADIATION