Now showing items 1-10 of 12

    • 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 ...
    • The awakening of BL Lacertae: observations by Fermi, Swift and the GASP-WEBT 

      Raiteri, C.M.; Villata, M.; Ammando, F.D.; Larionov, V.M.; Böttcher, 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 ...
    • 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 ...
    • Gamma–ray observational properties of TeV–detected blazars 

      Senturk, G.D.; Errando, M.; Böttcher, M.; Mukherjee, R. (IOP Science, 2013)
      The synergy between the Fermi-LAT and ground-based Cherenkov telescope arrays gives us the opportunity for the first time to characterize the high-energy emission from blazars over 5 decades in energy, from 100 MeV to 10 ...
    • How gravitational lensing helps y-ray photons avoid y-y absorption 

      Barnacka, Anna; Böttcher, Markus; Sushch, Iurii (IOP Publishing, 2014)
      We investigate potential γ – γ absorption of γ-ray emission from blazars arising from inhomogeneities along the line of sight, beyond the diffuse Extragalactic Background Light (EBL). As plausible sources of excess γ – γ ...
    • Leptonic and hadronic modeling of fermi–detected blazars 

      Böttcher, M.; Reimer, A.; Sweeney, K.; Prakash, A. (IOP Science, 2013)
      We describe new implementations of leptonic and hadronic models for the broadband emission from relativistic jets in active galactic nuclei in a temporary steady state. For the leptonic model, a temporary equilibrium between ...
    • A multiwavelength view of the flaring state of PKS 2155-304 in 2006 

      Abramowski, A.; Büsching, I.; De Jager, O.C.; Venter, C.; Vorster, M. (EDP Sciences, 2012)
      Context: Multiwavelength (MWL) observations of the blazar PKS 2155-304 during two weeks in July and August 2006, the period when two exceptional flares at very high energies (VHE, E ≳ 100 GeV) occurred, provide a detailed ...
    • Radio to gamma–ray variability study of blazar S5 0716+714 

      Rani, B.; Krichbaum, T.P.; Bottcher, M.; Lott, B.; Aller, H.D. (EDP Sciences, 2013)
      We present the results of a series of radio, optical, X-ray, and γ-ray observations of the BL Lac object S50716+714 carried out between April 2007 and January 2011. The multifrequency observations were obtained using several ...
    • Simultaneous multi-wavelength campaign on PKS 2005-489 in a high state 

      Venter, Christo; Vorster, Michael Johannes; Büsching, Ingo; De Jager, Ocker Cornelis (EDP Science, 2011)
      TeV γ-ray (H.E.S.S.), GeV γ-ray (Fermi/LAT), X-ray (RXTE, Swift), UV (Swift) and optical (ATOM, Swift) bands. This campaign was carried out during a high flux state in the synchrotron regime. The flux in the optical and ...