Now showing items 1-10 of 35

    • The 2010 very high energy γ-ray flare and 10 years of multi-wavelength observations of M 87 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Sheidaei, F.; Venter, C.; Vorster, M. (IOP Publishing, 2012)
      The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3 – 6) × 109 M☉) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) γ-ray ...
    • Attenuation of TeV γ-rays by the starlight photon field of the host galaxy 

      Zacharias, Michael; Chen, Xuhui; Wagner, Stefan J. (Oxford Univ Press, 2017)
      The absorption of TeV γ-ray photons produced in relativistic jets by surrounding soft photon fields is a long-standing problem of jet physics. In some cases, the most likely emission site close to the central black hole ...
    • The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT 

      Raiteri, C.M.; Böttcher, M.; Villata, M.; D'Ammando, F.; Larionov, V.M. (Oxford University Press, 2013)
      Since the launch of the Fermi satellite, BL Lacertae has been moderately active at γ-rays and optical frequencies until 2011 May, when the source started a series of strong flares. The exceptional optical sampling achieved ...
    • Characterizing the γ-ray long-term variability of PKS 2155-304 with H.E.S.S. and Fermi-LAT 

      Abdalla, H.; Barnard, M.; Böttcher, M.; Davids, I.D.; Garrigoux, T.; Ivascenko, A.; Krüger, P.P.; Pekeur, N.W.; Seyffert, A.S.; Spanier, F.; Sushch, I.; Van der Walt, D.J.; Van Rensburg, C.; Venter, C.; Wadiasingh, Z. (EDP Sciences, 2017)
      Studying the temporal variability of BL Lac objects at the highest energies provides unique insights into the extreme physical processes occurring in relativistic jets and in the vicinity of super-massive black holes. To ...
    • Discovery of a suspected giant radio galaxy with the KAT-7 array 

      Colafrancesco, S.; Oozeer, N.; Mhlahlo, N.; Jarrett, T.; Marchegiani, P. (Oxford Univ Press, 2016)
      We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the Wide-field Infrared Survey Explorer source J013313.50-130330.5, an extragalactic source based on its infrared ...
    • Discovery of TeV y-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift 

      Abramowski, A.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sheidaei, F.; Venter, C.; Vorster, M. (EDP Sciences, 2013)
      Very high-energy γ-ray emission from PKS 0447−439 was detected with the H.E.S.S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi bright source list and has ...
    • Discovery of very high energy γ-ray emission from the BL Lacertae object PKS 0301-243 with H.E.S.S. 

      Abramowski, A.; Böttcher, M.; Casanova, S.; Krüger, P.P.; Pekeur, N.W.; Sushch, I.; Venter, C.; Vorster, M. (EDP Sciences, 2013)
      The active galactic nucleus PKS 0301−243 (z = 0.266) is a high-synchrotron-peaked BL Lac object that is detected at high energies (HE, 100 MeV < E < 100 GeV) by Fermi/LAT. This paper reports on the discovery of PKS 0301−243 ...
    • Discovery of VHE gamma-rays from the high-frequency-peaked BL Lacertae object RGB J0152+017 

      Aharonian, F.; Büsching, I.; De Jager, O.C.; Holleran, M.; Raubenheimer, B.C.; Venter, C. (EDP Sciences, 2008)
      Aims. The BL Lac object RGB J0152+017 (z=0.080) was predicted to be a very high-energy (VHE; >100 GeV) $\gamma$-ray source, due to its high X-ray and radio fluxes. Our aim is to understand the radiative processes by ...
    • EBL inhomogeneity and hard-spectrum gamma-ray sources 

      Abdalla, Hassan; Böttcher, Markus (American Astronomical Society, 2017)
      The unexpectedly hard very-high-energy (VHE; E > 100 GeV) γ-ray spectra of a few distant blazars have been interpreted as evidence of a reduction of the γγ opacity of the universe due to the interaction of VHE γ-rays with ...
    • Energy loss in intergalactic pair beams: particle-in-cell simulation 

      Kempf, A.; Kilian, P.; Spanier, F. (EDP Sciences, 2016)
      Aims. The change in the distribution function of electron-positron pair beams determines whether GeV photons can be produced as secondary radiation from TeV photons. We will discuss the instabilities driven by pair ...